Talk:Book - A textbook of histology, including microscopic technic (1910) Special Histology 1
I. BLOOD AND BLOOD-FORMING ORGANS, HEART, BLOOD-VESSELS, AND LYMPH-VESSELS
A. BLOOD AND LYMPH.
J. FORMATION OF BLOOD.
EARLY in the development of the embryo there appear in a portion of the extra-embryonic area of the blastoderm, known as the area vasculosa, definite masses of cells, derived from the mesenchyme, and spoken of as blood islands, which are intimately connected with the formation of the blood. If these blood islands be examined at a certain stage, free cells are seen lying in their center, apparently derived from the central cells of the islands ; the cells surrounding them represent the elements which later go to form the primitive vascular walls. The free elements are the first blood-cells of the embryo. The blood-cells thus developed enter the circulation by means of blood channels formed by the confluence of the blood islands. These grow toward the embryo and later join the large central vessels. The origin of these blood islands is still an open question. Some authors contend that they arise from the mesoblast (P. Mayer, 87, 93 ; K. Ziegler ; van der Stricht, 92), others that they are of entodermic origin (Kupffer, 78 ; Gensch ; Riickert, 88 ; C. K. Hoffmann, 93, I ; 93, II ; Mehnert, 96). At a certain period the embryonic blood consists principally of nucleated red cells, which proliferate in the circulation by indirect division. The colorless blood-cells, the development of which is not yet fully understood, appear later. It is possible that they also are elements of the blood islands, which do not contain any hemoglobin. In a later period of embryonic life the liver becomes a blood-forming organ. Recent investigations have, however, shown that it does not take a direct part in the formation of the blood, but only serves as an area in which the blood-corpuscles proliferate during their slow passage through its vessels. The blind sac-like endings of the venous capillaries seem to be particularly adapted for this purpose, as in them the blood current stagnates, and it is here that the greater number of blood-cells reveal mitotic figures. The newly formed elements are finally swept away by the blood stream and enter the general circulation (van der Stricht, 92 ; v. Kostanecki, 92, III). Many investigators believe that the red blood-cells
1 86
BLOOD AND LYMPH. l8/
have an entirely different origin in the liver namely, from the large polynuclear, giant cells, which are thought to arise either from the cells of the capillaries or from the liver-cells (Kuborn, M. Schmidt).
Late in fetal life and in the adult, the red bone-marrow and the spleen are the organs which form the red blood-cells. The lymphatic glands and the spleen produce the white blood-cells. In addition to the nucleated red corpuscles which are present up to a certain stage of development, nonnucleated red blood-cells also appear. The number of the latter increases, until finally they are found almost exclusively in the blood of the new-born infant.
The blood of the adult consists of a fluid, coagulable substance, the blood plasma, and of formed elements suspended in this intercellular substance. The fluid medium of the blood is of a clear yellowish color and of alkaline reaction, having a specific gravity of about 1030. It is made up of water, of which it contains about 90 % , and various organic and inorganic substances. The formed elements are : (a) Red blood-corpuscles (erythrocytes) ; () white blood-corpuscles (leucocytes); and (r) the blood platelets of Bizzozero (82), hematoblasts of Hayem, or the thrombocytes of Dekhuysen. Besides these, there are present particles of fat, and, as H. F. Miiller (96) has recently shown, also hemokonia.
2. RED BLOOD-CORPUSCLES.
In man and nearly all mammalia the great majority of the red blood-corpuscles are nonnucleated, biconcave circular discs with rounded edges. They have smooth surfaces, are transparent, pale yellowish-red in color, and very elastic. No method has as yet been devised to demonstrate a nucleus in these cells, and there is no doubt that the red blood-discs of the human adult and of mammalia are devoid, in the histologic sense, of a nucleus capable of differentiation (compare Lavdowsky; Arnold, 96). They are therefore peculiarly modified cells. They possess a somewhat more resistant external zone of exoplasm, which has been interpreted as a cell membrane by certain observers (Lavdowsky), but which does not present the characteristics of a true cell membrane.
If fresh blood be left for some time undisturbed, the blood-discs adhere to each other by their flattened surfaces, grouping themselves in rouleaux,
By certain reagents the clear and transparent contents of the blood-corpuscles can be separated into two substances a staining and a nonstaining. The first consists of the blood pigment, or hemoglobin, which can be dissolved ; the second of a colorless substance, the strorna, which presents itself in various forms (protoplasm of the cell). The stroma probably contains the hemoglobin in solution.
Hemoglobin is a very complex proteid which may be decomposed into a globulin and a pigment hematin. The hemoglobin of the majority of animals crystallizes in the form of rhombic prisms ;
1 88 BLOOD AND BLOOD-FORMING ORGANS.
in the squirrel, however, in hexagonal plates, and in the guinea-pig in tetrahedra. Hematin combines with hydrochloric acid to form hemin, or Teichinanris crystals, of brownish color, rhombic shape, and microscopic size. They are of much value in lego-medical work, since they may be obtained from blood, no matter how old, and are characteristic of hemoglobin. They may be obtained from very small quantities of blood pigment.
If a small drop of blood pressed from a small puncture is placed on a slide and covered with a cover-glass, the red bloodcells soon become changed. This is due to the evaporation of water in the blood plasma, causing an increased concentration of the sodium chloride contained, which in turn draws water from the blood-cells The shrinkage which follows produces a characteristic
Fig. 151. Hu- Fig. 152. So-called Fig. 153. Hemin, or
man red blood-cells; "rouleau" formation of Teichmann's crystals, from
X 1500: a, As seen human erythrocytes ; X blood stains on a cloth,
from the surface ; 6, 1500. as seen from the edge.
Fig. 154. " Crenated" human red blood- Fig. 155. Red blood-corpuscles sub
cells; X 1500. jected to the action of water; X 1 5: a,
Spheric blood -cell ; b, "blood shadow."
change in the form of the cells, which assume a crenated or stellate shape. The red blood-cells of blood mounted in normal salt become crenated in a short time for the same reason. Red bloodcells are variously affected by different fluids. In water they become spheric and lose their hemoglobin by solution. Their remains then appear as clear, spheric, indistinct blood shadows, which may, however, be again rendered distinct by staining with iodin. Dilute acetic acid has a similar but more rapid action, with this peculiarity, that before becoming paler the blood-cells momentarily assume a darker hue. Bile, even when taken from the animal furnishing the blood, exerts a peculiar influence upon the red blood-cells ; they first become distended, and then suddenly appear to explode into
BLOOD AND LYMPH.
189
small fragments. Dilute solutions of tannic acid cause the hemoglobin to leave the blood-cells, and coagulate in the form of a small globule at the edge of the blood-cell. In alkalies of moderate strength the red blood-cells break down in a few moments.
Besides the disc-shaped red blood-cells, every well-made preparation shows a few small, spheric, nonnucleated cells containing hemoglobin. These, however, have received as yet but little attention.
M. Bethe makes the statement that human blood and the blood of mammalia contain corpuscles of different sizes, bearing a definite numerical relationship to each other. " If they be classified according to their size, and the percentage of each class be calculated, the result will show a nearly constant proportional graphic curve varying but slightly, according
o
Fig. 156. Red blood-corpuscles from various vertebrate animals; X IOO (Walker's model) : a, From proteus (Olm) ; b, from frog ; c, from lizard ; d, from sparrow ; e, from camel ; /and^-, from man ; h, from myoxus glis ; i, from goat ; k, from musk-deer.
to the animal species." According to M. Bethe, dry preparations of human and animal blood may be distinguished from each other, with the exception of the blood of the guinea-pig which presents a curve identical with that of human blood.
The red blood-cells of mammalia, excepting those of the llama and camel species, are in shape and structure similar to those of man. The red blood-cells of the llama and camel have the shape of an ellipsoid, flattened at its short axis, but also nonnucleated.
We have already made mention of the fact that the embryonal erythrocytes are nucleated ; the question now arises as to how, in the course of their development, they lose their nuclei. Three possibilities confront us : First, either the embryonal blood-cells are destroyed and gradually replaced by previously existing nonnucle
190 BLOOD AND BLOOD-FORMING ORGANS.
ated elements ; or, second, the nonnucleated red cells are formed from the nucleated by an absorption of the nucleus (or what appears to be such' to the eye of the observer, Arnold, 96) ; or, finally, the nucleus is extruded from the original nucleated cell. According to recent investigations (Howell) the third possibility represents the change as it actually takes place.
In all vertebrate animals except mammalia, the red bloodcorpuscles are nucleated. They are elliptic discs with a biconvex center corresponding to the position of the nucleus. The bloodcells of the amphibia (frog) are well adapted for study on account of their size. They are long and, as a rule, contain an elongated nucleus with a coarse, dense chromatin framework, which gives them an almost homogeneous appearance. The cell-body may be divided, as in mammalia, into stroma and hemoglobin. When subjected to certain reagents, the contour of the cells appears double and sharply defined. This condition is, however, no proof of the existence of a membrane. The blood-cells of birds, reptiles and fishes are similarly constructed.
The diameter of the erythrocytes varies greatly in different vertebrate animals, but is constant in each species. The red blood-cells of man measure on the average 7.5 // (7.2 fj. to 7.8 //), in their long diameter, and I.6// to 1.9^ in their short diameter. We append a table of their number in a cubic millimeter and size in man and certain animals as compiled by Rollett (71, II) and M. Bethe :
,
No. IN
SPECIES.
SIZE.
CUBIC MILLI
METER.
Man
. . . (Homo]
. 7.2-7.8^
. . . 5,000,000
Monkey
. . . (Cercopith. ruber)
70
. . . 6,355,000
Hare
. . . (Lepus cuniculus)
. 7.16 .
. . . 6,410,000
Guinea-pig ....
. . . (Cavia cob.) ....
. 7-48
. . . 5,859,5oo
Dog
. . . (Cam's fam.) ....
. 7-2 .
. . . 6,650,000
Cat
. . . (Felis dom.) ....
. 6.2 .
. . . 9,900,000
Horse
. . . (Equus cab.) ....
5-58
7,403,50
Musk-deer ....
. . . (Moschus jav.) . . .
2.5
Spanish goat . . .
. . . (Capra /its.) ...
.4.25 .
. . . 19,000,000
Domestic chaffinch .
. . . (Fringilla dom. ) . .
. Length,
11.9
Breadth,
6.8
Dove
. . (Columba)
L.
14.7 .
. . . 2,010000
B.
6-5
Chicken
. . . ( Callus dom. ) . . .
. L.
12. 1
B.
7.2
Duck
. . . (Anas bosch.) . . .
. L.
12.9
B.
8.0
Tortoise
. L.
21.2 .
. . . 629,000
B.
12.45
Lizard
. . . (Lacerta agil.) . . .
. L.
15-75
. . . 1,292,000
B.
9-1
Snake
. . . (Coluber natr.) . . .
. L.
22. .
. . . 829,400
B.
13.0
Frog
. . . (Hana temp.) . . .
. L.
22.3 .
. . . 393,200
B.
15-7
Toad
. . . (Bufo vulg.) ....
. L.
21.8 .
. . . 389,000
B.
15-9
Triton
. . . (Triton crist.) . . .
. L.
29-3
. . . 103,000
B.
19-5
BLOOD AND LYMPH.
Salamander
No. IN
SIZE. CUBIC MILLI METER.
Length, 37.8 80,000
Breadth, 23.8
L. 58 35,ooo
B. 35
L. 13.4
B. 10.4
Carp (Cyprinus Gobio) . . . L. 17.7
B. 10. i
SPECIES.
(Salamandra mac.}
(Proteus angu.) Sturgeon (Acipenser St.) . .
3. WHITE BLOOD-CORPUSCLES.
The white blood-cells contain no hemoglobin and are nucleated elements which, under certain conditions, possess ameboid movement. Their size varies from 5 fj. to 12 //, and they are less numerous than the red blood-corpuscles, one white blood-cell to from three hundred to five hundred red cells being a normal proportion.
Fig. 157. From the normal blood of man; X I2O (from dry preparation of H.
F. Miiller) : a, Red blood-cell ; b, lymphocyte ; c and d, mononuclear leucocytes ; e t
transitional leucocyte ; f and g, leucocytes with polymorphous nuclei.
Flemming ascribes a fibrillar structure to the protoplasm of white blood-cells, and was the first to observe a centrosome situated near the nucleus. M. Heidenhain made the observation that the white blood-cells possessed several centrosomes grouped to constitute a microcenter (microcentrum) about which the fibrillar structure of the protoplasm was arranged radially." The meshes of the fibrillar network are filled with a more fluid interfibrillar substance, in which are found the specific granules to be mentioned later. In the normal blood the white blood-cells vary in size and structure, and the following varieties are distinguished : (i) Small and large lymphocytes ; (2) mononuclear leucocytes ; (3) transitional leucocytes ; (4) leucocytes, either polymorphonuclear or polynuclear.
The lymphocytes form about 20% of the white blood-cells.
1 92 BLOOD AND BLOOD-FORMING ORGANS.
They vary in size from 5 // to 7. 5 fj. and possess a relatively large nucleus, the chromatin of which is in the form of relatively large granules, which stain rather deeply. The nucleus is surrounded by a narrow zone of protoplasm, often seen clearly only to one side of the cell in the form of a crescent. It does not stain readily in acid dyes.
The leucocytes vary in size from 7 /j. to 10 fi. The mononuclear leucocytes, constituting about 2^ to 4^ of the white blood-cells, have a nearly round or oval nucleus, which usually does not stain very deeply, and which is relatively smaller than that of the lymphocytes. The transitional leucocytes, forming also about 2 ^ to 4^ of the white blood-cells, are developed from the mononuclear variety and represent transitional stages in the development of mononuclear leucocytes to those with polymorphous nuclei. The nucleus in the transitional form is similar in size and structure to that of the mononuclear variety, but Of a more or less pronounced horseshoe-shape. The leucocytes with polymorphous miclei, developed from the transitional forms, are very numerous in the blood, forming about 70^ of the entire number of white blood-cells. They are also the cells which show the most active ameboid movement when examined on the warm stage. They possess variously lobulated nuclei, the several nuclear masses often being united by delicate threads of nuclear substance. A leucocyte with a polymorphous nucleus becomes a polynu clear cell in case the bridges of nuclear substance uniting the several lobules of the nucleus break through. In the protoplasm of the transitional leucocytes, the polymorphonuclear, and the polynuclear forms are found fine and coarse granules. Our knowledge of these granules has, however,
at /3yd
Fig. 158. Ehrlich's leucocytic granules; X '800 (from preparations of H. F. Miiller) : a, Acidophile or eosinophile granules, relatively large and regularly distributed ; e, neutrophile granules ; /3, amphophile granules, few in number and irregularly distributed ; y, mast cells with granules of various sizes ; t!, basophile granules, (a, 6, and e, From the normal blood ; y, from human leukemic blood ; /3, from the blood of guinea-pig.)
been greatly extended since Ehrlich has shown that the granules of leucocytes show specific reactions toward certain anilin stains, or combinations of such stains. He divides the granules of the leucocytes into five classes which he terms respectively a-, (3-, 3-, ?-, and egranules. In human blood are found the a-granules, which show an affinity for acid-anilin stains, are therefore known as acidophile gran
BLOOD AND LYMPH. 1 93
ules, and, since they are most readily stained in eosin, are generally spoken of as eosinophile granules. In normal blood from I ^ to 4^ of the polymorphonuclear leucocytes and now and then a transitional cell have eosinophile granules. The granules are coarse and stain bright red in eosin. Nearly all the leucocytes with granules (from 65 ^ to 68 % of all white blood-cells) have e-granules or, since they are stained in color mixtures formed by a combination of acid and basic anilin stains, neutropliile granules. The neutrophile granules are much finer than the eosinophile and are not stained in acid stains. The y- and ^-granules are stained in basic anilin stains, and are known as basophile granules. They are coarse and irregular, and the leucocytes containing them form from o. 5 % to I <fo of the white blood-cells.
It cannot at this time be definitely stated whether the different varieties of granules are to be looked upon as specific products of the protoplasm of the leucocytes, possibly of the nature of granules which may be likened to the secretory granules of glandular cells, or whether they are to be regarded as cell inclusions. It has also not been clearly shown whether one variety of granules may develop into another variety, neutrophile into eosinophile, although this has been suggested. According to Weidenreich, eosinophile granules are thought to represent fragments of erythrocytes, enclosed within the protoplasm of leucocytes.
The polymorphism of the leucocyte-nucleus has induced many investigators to advance the theory that a direct division takes place (fragmentation Arnold, Lowit). Flemming (91, III), however, succeeded in demonstrating that true rnitotic processes actually take place, so that in this respect there really exists no difference between leucocytes and other cells (compare also H. F. Miiller, 89, 91). It is only in the formation of polynuclear leucocytes that the polymorphous nucleus sometimes undergoes a fragmentation process which results in several parts. But even in this case pluripolar mitoses have been observed. A division of the cell-body subsequent to that of the nucleus is lacking in the processes just described. As a result a single cell with several nuclei is formed (polykaryocyte). The fate of such cells is still in doubt.
The extraordinary motility which most leucocytes possess, is in great part responsible for their wide distribution, even outside of the vascular system. They have the power of creeping through the walls of the capillaries (diapedesis, Cohnheim 67, I), and of penetrating into the smallest connective-tissue clefts, between the cells of epithelia, etc., whence they either pass on (migratory cells) or remain stationary for a time. An important function falls to the lot of the leucocytes in the absorption of superfluous tissue particles or in the removal of foreign bodies from certain regions of the body. In the first case they take part in a process of tissue-disintegration ; in the second, they take up the particles by means of their pseudopodia for the purpose either of assimilation or of removal (phago'3
194 BLOOD AND BLOOD-FORMING ORGANS.
cytes). It may be readily understood that the latter function of the leucocytes is of the greatest importance in certain pathologic processes.
It is somewhat venturesome at the present state of our knowledge to make definite statements as to the origin in postembryonic life of the various forms of white blood-cells above described. The following statement, however, seems warranted from the evidence at hand.
The lymphocytes would seem to be developed in the meshes of adenoid tissue, especially in the so-called germ centers of Flemming, m the adenoid tissue of lymph-glands and lymph-follicles (see under these). Here the cells undergo active karyokinetic division, but where the cells which pass through the process originate is a matter concerning which there is a difference of opinion. Some investigators believe that they penetrate the germ centers with the lymph, and find there a suitable place for division. Again, others see in Flemming's germ centers permanent organs whose elements remain stationary and supply the blood with a continuous quota of lymphocytes. Be this as it may, the fact remains that the germ centers are the most important regions for the formation of lymphocytes. From these they pass out with the lymph current into the blood circulation, or directly into the blood-vessels, there to enter upon the functions which they are called upon to perform. The leucocytes with neutrophile granules are probably developed in the blood and lymph from mononuclear leucocytes which have their origin in the spleen pulp, possibly also in trie bone-marrow. The leucocytes of circulating blood with eosinophile granules in all probability come from mononuclear cells with such granules found in bone-marrow. Under certain conditions it would seem that they also develop in connective tissue. The leucocytes with the basophile granules probably enter the circulation from the connective tissue of certain regions. The lymphocytes and leucocytes found in the blood are also found in the lymph-vessels and lymph-spaces.
4. BLOOD PLATELETS THROMBOCYTES.
The third element of the blood is the blood platelets (Bizzozero) (blood-placques, Laker ; hematoblasts, Hayem ; thrombocytes, Deckhuysen). They are extremely delicate and transitory structures, whose existence in the living blood was denied for a long time by many investigators, but whose presence in the wing vessels of the living bat was conclusively demonstrated by Laker (84). They are free from hemoglobin, are of round or oval shape, and in mammals measure about 3 p. in diameter. Owing to the fact that they readily clump together when blood leaves the vessels, and undergo change, it is somewhat difficult to give an estimate of their number. They are said to be present in human blood to the extent of 200,000 to 300,000 in every cubic millimeter. By the exercise of great care
BLOOD AND LYMPH.
195
and the employment of special methods on the part of a number of recent observers (Detjen, Deckhuysen, Kopsch and Argutinsky), they have been able to show that these structures present a more complicated structure than was formerly thought. When examined in an isotonic salt solution (for mammals 0.9 to 0.95 sodium chlorid solution), they present an oval or short spindle-shaped form, and in them there can be made out a relatively large structure, which stains in certain basic aniline stains and is interpreted as a nucleus (Deckhuysen). When examined after a method suggested by Detjen (with a i per cent, agar solution there is mixed O.6 per cent, sodium chlorid, 0.3 per cent, of sodium metaphosphate and dipotassiuin phosphate; a thin layer of this agar mixture is spread on the slide and a drop of blood mounted between it and the cover), the blood platelets or thrombocytes may be observed on the warm stage for several hours, and it may be seen that they present ameboid movement, in that short, thread-like processes pass out from the cell, which may alter their shape and position and which may be again withdrawn.
When the blood leaves the bloodvessels, the blood platelets or thrombocytes break down very quickly, unless the above-mentioned methods are made use of, so that in ordinary
fresh preparations or generally in dried films they are not to be observed in an unaltered state. The nuclei disappear and the protoplasm becomes granular or vacuolated. The breaking down of the blood platelets or thrombocytes is accompanied by the formation of fibrin (coagulation of the blood), the fibrin threads beginning at the borders or processes of the platelets, and radiating in all directions (Kopsch).
Hemokonia. H. F. Muller (96) found in the blood of healthy and diseased individuals highly refractive, colorless, and round (seldom rodlike) bodies, which he terms " hemokonia. " Their numbers vary, although they are normal constituents of the blood. Their nature and origin are obscure. They do not dissolve in acetic acid, nor are they blackened by osmic acid. The latter would seem to indicate that they do not consist of ordinary fat substance, although they are probably composed of a substance closely allied to fat. They are usually i p. in diameter.
Fig. 159- Fibrin from laryngeal
vessel of child ; X about 30x3.
196 BLOOD AND BLOOD-FORMING ORGANS.
5. BEHAVIOR OF BLOOD-CELLS IN THE BLOOD CURRENT.
In the circulating blood the behavior of the formed elements varies. The more rapid axial current contains very nearly all the erythrocytes, and as a consequence very few are found adjacent to the walls of the vessels. In the peripheral current, on the other hand, are found most of the leucocytes, and in a retarded circulation they are seen to glide along the walls of the vessels. At the bifurcations of the vessels, especially of the capillaries, the erythrocytes are sometimes caught and elongated by the division of the current, the one-half of the cell extending into the one and the other half into the other branch of the vessel, while the corpuscle oscillates back and forth. When again free the cell immediately resumes its original shape. From this it is seen that erythrocytes are very elastic structures. In the smaller vessels and capillaries, especially when the latter are altered by pathologic conditions, the leucocytes may be seen passing out of the vessels, and it would seem that they are able to penetrate through the walls and even through the endothelial cells lining the blood-vessels (compare also Kolossow, 93). First, they send out a fine process, which is probably endowed with a solvent action. This penetrates the wall of the vessel, after which the remainder of the cell pushes its way through slowly.
B. LYMPHOID TISSUE, LYMPH-NODULES, AND LYMPHGLANDS.
As to the origin of lymphoid tissue, the lymph-glands, and the spleen, there is still considerable difference of opinion. Most authors believe that these structures are developed from the middle germinal layer (Stohr, 89 ; Paneth ; J. Schaffer, 91 ; Tomarkin). Others believe in an entodermic origin (Kupffer, 92 ; Retterer ; Klaatsch ; C. K. Hoffmann, 93, II).
The framework of lymphoid tissue is a reticular connective tissue (adenoid connective tissue His, 61). This consists of a network of fine fibrils of reticular and white fibrous connective tissue aftd of cells (endoplasm and nuclei) which are situated on the reticulum, often at nodal points. Within its meshes the lymph-cells lie in such numbers and so densely arranged that on microscopic examination the network is almost entirely covered unless very thin sections are used. The cells may be removed from the meshes of the reticulum by stippling and brushing section with a fine brush or by placing sections in a test-tube partly filled with water and subjecting them to vigorous shaking, or, still better, by subjecting sections or pieces of lymphoid tissue to digestion with pancreatin.
Lymph tissue may be diffuse, as in the mucous membrane of the air-passages and as in that of the intestinal tract, uterus, etc. (vid. Sauer, 96). Lymphoid tissue may be also sharply defined in the
LYMPHOID TISSUE, LYMPH -NODULES, AND LYMPH-GLANDS. 197
form of round nodules, simple follicles or nodules. These are either single, solitary lymph-follicles, or gathered into groups, agminated lymph -nodules. They are found scattered in the mucous membrane of the mouth, pharynx, and intestine. In lymph-nodules also we find the characteristic lymph-cells and the adenoid reticulum. As a rule, the former are arranged concentrically at the periphery ; and in the center of the nodule the reticular tissue usually has wider meshes, and the lymph-cells are less densely placed. (Fig. 160.) In the center of the nodule the cells often show numerous mitoses, and it is here that an active proliferation of the cells takes place. The cells may either remain in the lymph-follicle or the newly formed cells are pushed to the periphery of the nodule, and are then swept into the circulation by the slow lymph current which circulates between the wide meshes of the reticular connective tissue. Flemming (85, II) has called that central part of the nodule containing the proliferating cells the germ center or secondary nodule (compare p. 194). The germ centers are transitory structures, and are consequently found in different stages of development. They may even be absent for a time.
-Epithelium
of intestine. a
Fig. 160. A solitary lymph-nodule from the human colon. At a is seen the pronounced
concentric arrangement of the lymph-cells.
The lymph-glands are organs of a more complicated structure, but also consist of lymphoid tissue. They are situated here and there in the course of the lymph-vessel and are widely distributed. Their size varies greatly. In shape they are much like a bean or kidney, and the indentation on one side is known as the hilum. The afferent lymph-vessels, the vasa affercntia, enter at the convex surface of the organ, while the efferent vessels, the vasa efferentia, pass out
198
BLOOD AND BLOOD-FORMING ORGANS.
at the hilum. The whole gland is surrounded by a capsule consisting of two layers : the outer is made up of a loose, and the inner of a more compact, connective tissue in which elastic fibers and a few smooth muscle-fibers are imbedded. Portions of the inner layer pass into the substance of the gland to form septa, or trabeculce, by means of which the organ is divided into a number of imperfectly separated compartments. These trabeculae may be very well developed, as in the lymph-glands of the domestic cattle, or only
Fig. 161. Transverse section of human cervical lymph-gland, showing the general
structure of a lymph-gland ; X J 8. Af> Blood-vessels ; ff, fibrous capsule ; h, hilum ;
kz, germ-center ; nl, lymph-nodule ; sc, cortical substance ; gm, medullary substance ;
tr, trabeculse ; via, afferent lymph-vessels ; vie, efferent lymph-vessels ( " Atlas and
Epitome of Human Histology," Sobotta).
poorly developed, as in the human lymph-glands, where they are often almost wanting. The lymphoid tissue of the gland is so distributed that at its periphery a large number of more or less clearly defined lymph-nodules are found, which are in part separated from each other by the trabeculae just described, the cortical nodules. The nodules are structural units and have a typical blood supply, and are in structure like the lymph-nodules of simple and ag
LYMPHOID TISSUE, LYMPH-NODULES, AND LYMPH-GLANDS. 199
minated follicles above mentioned. They form a peripheral layer which is, however, not clearly defined in the neighborhood of the hilum. This layer is known as the cortex of the lymph-gland. (Fig. 161.) The lymphoid tissue of the interior of the gland, the medullary substance, is in the shape of cords medullary cords which are continuous with the lymphoid nodules of the cortical portion. These connect with each other and form a network of lymphoid tissue, in the open spaces of which lie the trabeculae. At their periphery the nodules and medullary cords are bordered by a wide-meshed lymphatic tissue, the lymph-sinus of the gland, parts of which lie (i) between the capsule and the cortical substance, (2)
Mitosis.
Germ center.
Lymph-sinus.
^SSS^sk"*"*?^
- t *JW*V - *-*^ e *
Medullary cord.
Fig. 162. From a human lymph-gland ; X 2 4- At a are seen the concentrically arranged cells of the lymph-nodules. (Fixation with Flemming's fluid.)
between the nodules of the latter and the trabeculae, (3) between the medullary cords and the trabeculae, and (4) between the medullary substance and the capsule at the hilum. At the hilum the loose lymphoid tissue represents a terminal sinus (Toldt). These sinuses are lined throughout by endothelial cells, which are continuous with those of the afferent and efferent lymph-vessels. The lymph flows into the gland through the afferent vessels, and passes along into the interior through the spaces offering the least resistance (sinuses). The latter represent those peripheral portions of the nodules and of the medullary cords in which the lymphoid tissue is present in Joose arrangement. The lymph consequently envelops
2OO THE BLOOD AND BLOOD-FORMING ORGANS.
not only the lymph-nodules of the cortical substance, but also the medullary cords, and finally streams into the terminal sinus and then into the efferent channels. As a result the lymph takes with it the newly formed cells of the lymph-nodules and the medullary cords, and passes out richer in cellular elements than on its entrance.
The lymph-glands receive their blood supply mainly through the hilum ; relatively small arterial branches may penetrate the capsule. Generally, a number of arterial branches enter at the hilum, from whence they may pass directly into the medullary substance, or pass for a distance in trabeculae. In their course branches are given off which pass to the medullary cords, in which they break up into capillary vessels situated in the periphery of the cords. These unite to form small veins which anastomose freely, and unite to form larger veins. The cortical nodules receive their blood supply from arterial branches which enter their proximal sides (side toward the hilum) and course through the center of the nodules, giving off capillary vessels which pass, without much anastomosis, to the periphery of the nodules, where they unite to form plexuses ; the capillaries of these plexuses join to form the veins of the nodules, which are thus situated at their periphery. These veins unite to form larger veins, which leave the glands at the hilum (Calvert).
Medullated and nonmedullated nerves penetrate the lymphglands accompanying the blood-vessels on which they terminate.
Hemolymph Glands. A typical lymph-gland possesses afferent and efferent lymph-vessels and a closed blood-vascular system completely separated from the lymph -vascular system, as may have been seen from the foregoing description. Attention has, however, been called in recent years to certain lymph -glands in which the complete separation of the vascular and lymphatic systems does not obtain, glands in which the formed elements of blood and lymph are intermingled in the meshes of the adenoid reticulum, and which contain blood-sinuses in place of the lymph-sinuses observed in the typical lymph-glands. These have been designated as hemolymph glands (Blutiymphdrusen, hemal glands, hemal lymphatic glands). In the typical hemolymph glands there are no afferent and efferent lymphatic vessels; the. glands are intercalated in the vascular system. Certain less clearly defined hemolymph glands possess afferent and efferent lymphatics and bloodsinuses, the two systems being not completely separated. These may be considered transitional forms.
Lymph-glands with blood-sinuses were first described by Gibbes, who found such glands in the region of the renal artery. They were further considered and more fully described by Robertson, to whom the term hemolymph glands is to be credited, and by Clarkson, Vincent and Harrison, Drummond, Warthin, Weidenreich and Lewis. It appears from their description that they are widely distributed among vertebrates, although not equally well developed
LYMPHOID TISSUE, LYMPH-NODULES, AND LYMPH-GLANDS. 2OI
in the different types studied. Warthin has discussed more fully than other observers the hemolymph glands of man, and his account will here be followed in the main. It may be parenthetically stated that the hemolymph glands are numerous and well developed in the sheep (Warthin, Weidenreich) ; not so well differentiated in the dog and cat ; on the other hand, well developed in the rat (Lewis).
We learn from the account of Warthin that the hemolymph glands are numerous in man, in the prevertebral retroperitoneal region, in the cervical region, and less numerous in the thorax. They vary in size from that of several millimeters to that of several centimeters. They present a variety of structure, depending mainly upon the arrangement of the lymphoid tissue and blood-sinuses. The great majority of these glands show a resemblance in structure to splenic tissue (splenolymph glands) ; others resemble more closely marrow-tissue (marrow lymph-glands). Between the two varieties of lymph-glands there are found transition forms, as also between these and lymph-glands (Warthin).
The hemolymph glands (splenolymph glands) are surrounded by a capsule varying in thickness and composed of white fibrous and elastic tissue and nonstriated muscle-cells. From it trabeculae of the same structure pass into the gland, which after division are lost in the substance of the gland. Beneath the capsule there is found a continuous or discontinuous blood-sinus, bridged over by reticular fibers, from which anastomosing sinuses pass to the interior of the gland. These blood-sinuses are, in part at least, lined by endothelial cells. The sinuses in the gland substance are also bridged by trabeculse and reticular fibers. The sinuses divide the lymphoid tissue into anastomosing masses and cords. This tissue consists of an adenoid reticulum, in the meshes of which are found white and red blood-cells. The small lymphocytes are numerous; next in frequency are found the rnononuclear leucocytes ; transitional and polymorphonuclear cells. Basophile and eosinophile cells are also found. According to Weidenreich, the eosinophile cells are numerous ; he is also of the opinion that the eosinophile granules are derived from disintegrating red blood-cells. In the reticulum and in the blood-sinuses are found mononuclear phagocytes, the origin of which has not been fully determined. Certain observers (Schumacher, Weidenreich) trace their origin to the cells of the reticulum ; Thoma regards them as developed from endothelial cells, while Drummond and others regard them as altered leucocytes. They contain disintegrating red blood-cells and pigment (according to Weidenreich, eosinophile cells). The majority of the hemolymph glands present a hilum through which the blood-vessels enter. The arteries, soon after entering the gland, divide into smaller branches, certain of which communicate directly through blood-capillaries with the blood-sinuses (Lewis) ; others pass to the adenoid tissue. The larger veins are in the trabeculae
2O2 BLOOD AND BLOOD-FORMING ORGANS.
(at the hilum). On leaving the trabeculae their walls are formed of endothelium and adenoid reticulum, which separates them from the blood-sinuses. They end (or begin) in lacunae with thin walls which are perforated and communicate with the blood-sinuses (Weidenreich). Nerves have been traced to the hemolymph glands by Lewis (dog, rat). They probably end in the involuntary muscle of the capsule and trabeculae. Typical hemolymph glands have no lymph-vessels. In certain glands both blood- and lymph-sinuses are found. In such glands there is apparently an intermingling of blood and lymph, so that red blood-cells may pass into the lymphatics.
The marrow lymph-glands are not so numerous. They have a thin capsule consisting of fibrous tissue but containing little elastic and muscular tissue. The blood-sinuses are not so well developed. In the lymphoid tissue the basophile and eosinophile cells are more numerous than in the splenolymph glands, and large cells similar to the large bone-marrow cells are now and then met with.
As appears from the accounts of the majority of observers who have studied hemolymph glands, they have a hemolytic function, in that the red blood-cells are destroyed in them. Robertson and Clarkson ascribe to them a blood-forming function. This has also been observed by Warthin in the case of marrow lymph-glands, under certain conditions. The hemolymph glands are seats of origin for the white blood-cells which appear also to be destroyed here (eosinophile cells, Weidenreich).
C THE SPLEEN.
The spleen is a blood-forming organ, in which white blood-cells and, in embryonic life and under certain conditions in adult life also, red blood-cells are formed the former in the adenoid tissue (Malpighian corpuscles) and spleen pulp, the latter only in the spleen pulp.
The spleen is covered by peritoneum, and possesses a capsule consisting of connective tissue, elastic fibers, and nonstriated musclecells. This capsule sends numerous processes or trabeculae into the interior of the organ, which branch and form a framework in which the vessels, especially the veins, are imbedded. This connective-tissue framework breaks up to form the reticular tissue which constitutes the ground substance of the spleen.
On examining a section of the spleen with the low-power magnifying glass, sections of the trabeculae, and round or oval masses of cells, having a diameter of about 0.5 mm., and in structure and appearance similar to the lymph-nodules (Malpighian corpuscles), are clearly defined ; between and around these structures is a tissue rich in cells, blood-vessels and blood-corpuscles, known as the spleen pulp.
THE SPLEEN.
203
The organ has a very typical blood supply. Its arteries enter at the hilum, or indented surface, and its veins pass out at the same place. On the penetration of the vessels through the capsule, the latter forms sheaths around them (trabeculse), but as soon as the arteries and veins separate, the trabeculae envelop the veins alone. The arteries break up into smaller branches, which in turn divide into a large number of tuft-like groups of arterioles. Soon after their separation from the veins, the adventitia (outer fibrous tissue coat) of
SOl
Fig. 163. Portion of section of human spleen ; X I 5- The figure gives a general
view of the structure of the spleen : a, Arteries with lymphoid sheaths ; cf, fibrous capsule ;
Mk, Malpighian corpuscle ; //, spleen pulp ; tr, trabeculae ; v, vein in trabecula ("Atlas
and Epitome of Human Histology," Sobotta).
the arteries begins to assume a lymphoid character. This lymphoid tissue increases here and there to form true lymphoid nodules, possessing all the characteristics already mentioned reticular tissue, germ centers, etc. These are the Malpighian bodies, or corpuscles ; they are not very plentifully represented in man. The Malpighian bodies with their germ centers are formative centers for the lymphocytes. The newly formed cells pass into the pulp and mix with its elements, which are then bathed by the blood emptying from the
2O4 BLOOD AND BLOOD-FORMING ORGANS.
arterial capillaries into the channels of the pulp. The lymphoid sheaths and nodules derive their blood supply from arteries which arise from the lateral branches of the splenic vessels, and which divide into capillaries inside of the lymph sheaths or nodules, and only assume a venous character outside of the lymphoid substance. These vessels constitute the nutritive vascular system of the spleen.
The small arterial branches above mentioned break up into very fine arterioles which gradually lose their lymphoid sheath, so that branches with a diameter of 0.02 mm. no longer possess a lymphoid sheath, but again assume an adventitia of the usual type. The smallest arterioles now pass over into capillaries which are for a time accompanied by the adventitia (capillary sheath), while the terminal branches have the usual structure of the capillary wall and are gradually lost in the meshes of the pulp. (See below.) On the other hand, the beginnings of the venous capillaries may be distinctly seen in the pulp spaces. Groups of these capillaries combine to form larger vessels, which, however, still retain a capillary structure, and these again form small veins which unite to form the larger veins.
F. P. Mall, whose recent contributions on the structure of the spleen have greatly extended our knowledge of the microscopic anatomy of this organ, states that the trabecular and vascular systems together outline masses of spleen pulp about i mm. in diameter, which he has named spleen lobules. Each lobule is bounded by three main interlobular trabeculae, each of which sends three intralobular trabeculae into the lobule which communicate with each other in such a manner as to divide the lobule into about ten smaller compartments. An artery enters at one end of the lobule and, passing up through its center, gives off a branch to the spleen pulp found in each of the ten compartments formed by the intralobular trabeculae. . The spleen pulp in these compartments is arranged in the form of anastomosing columns, or cords, to which Mall has given the name of pulp cords. The branches of the main intralobular artery, going to each compartment, divide repeatedly ; the terminal branches course in the spleen-pulp cords, and in their path give off numerous small side branches which end in small expansions known as the ampulla of Thoma. An ampulla of Thoma may be divided into three parts. The first part, which is the ampulla proper, is lined by spindle-shaped cells, directly continuous with the endothelial cells of the artery. The second third, which often communicates with neighboring ampullae, contains large side -openings. The remaining third, which is the intermediary segment of Thoma (Thoma 's Zivisckenstuck], is difficult to demonstrate. It is bridged over by fibrils of reticulum, and its communication with the vein is not wide. The circulation through the spleen is therefore not a closed one, through a system of capillaries completely closed, but rather through spaces in the spleen -pulp, certain of which are more direct, leading from the terminal arteries to the veins. According to this view, then,
THE SPLEEN.
2O5
"the blood passes from the ampullae into the pulp spaces, then through the pores into the walls of the veins to form columns of blood discs which are pushed from the smaller to the larger veins of the spleen." The pulp spaces usually contain very few bloodcorpuscles, in preparations fixed and prepared in the usual way, since on removal from the animal the muscular tissue of the capsule and trabeculae contracts and presses the blood from pulp spaces into the veins. If, however, the muscular tissue of the spleen is paralyzed before the tissue is fixed, numerous blood-corpuscles are found in the pulp spaces. In the above account of the ultimate distribution of the splenic vessels we have followed very closely the recent observations of F. P. Mall. The accompanying diagram (Fig. 164), slightly, though immaterially, modified from one given
Capsule.
Intralobular trabecula. - I i
Artery to one of the ten compartments.
Intralobular artery. : Interlobular trabecula. - Intralobular trabecula ,
Malpighian corpuscle.
-- Intralobular venous
spaces. I Intralobular vein.
- Ampulla of Thoma.
Spleen pulp cord.
Interlobular vein.
Intralobular vein.
l-'ig. 164. Diagram of lobule of the spleen (Mall, "Johns Hopkins Hospital Bulletin," Sept., Oct., 1898).'
by F. P. Mall, shows clearly the trabecular and vascular systems of a spleen lobule. In larger spleens there may be some two hundred thousand of these lobules. In a dog weighing 10 kg. there are on an average some eighty thousand (F. P. Mall).
The splenic pulp consists of a reticulum, in the meshes of which are found (i) fully developed red blood-cells; (2) now and then nucleated red blood-cells; (3) in many animals giant cells ; (4) cells containing red blood-corpuscles and the remains of such, with or without pigment ; (5) the different varieties of white blood-cells, especially a relatively large proportion of mononuclear leucocytes. Pigment granules, either extra- or intracellular, also occur in the splenic pulp. The pigment probably originates from disintegrating erythrocytes. Besides these are found, especially in
2O6
BLOOD AND BLOOD-FORMING ORGANS.
teased preparations, long, spindle-shaped and flat cells, which are probably derivatives of the connective-tissue cells of the pulp and of the endothelium and muscular fibers of the vessels.
Fig. 165. Cells containing pigment, blood-corpuscles, and hemic masses from the spleen of dog ; X 1800 (from cover-glass of H. F. Miiller).
Fig. 1 66. From the human spleen ; X 8 (chrome-silver method) : a, Larger fibers
of a Malpighian body ; b, reticular fibrils (Gitterfasern).
In embryonic life and under certain conditions in postembryonic life (after severe hemorrhage and in certain diseases) red blood-cells are developed in the spleen pulp. The nucleated red blood-cells
THE BONE-MARROW. 2O/
from which they develop may lose their nuclei in the spleen pulp or only after entering the circulation (compare Bone-marrow).
Lymphatic vessels have been observed in the capsule and trabeculae, but not in the spleen pulp nor Malpighian corpuscles.
The spleen receives medullated and nonmedullated nerve-fibers ; the latter are much more numerous. The medullated nervefibers are no doubt the dendrites of sensory neurones. Their mode of ending has, however, not been determined. It is probable that they will be found to terminate in the fibrous-tissue coat of the vessels, and in the trabeculae and capsule. The nonmedullated nerve-fibers, no doubt the neuraxes of sympathetic neurones, are very numerous ; they enter the spleen with the artery and mainly follow its branches. By means of the chrome-silver method, Retzius (92) has shown that in the rabbit and mouse these nervefibers follow the vessels, forming plexuses which surround them, the terminal branches of these plexuses terminating in free endings in the muscular coat of the arteries. Here and there a nerve-fiber could be traced into the spleen pulp. The mode of ending of such fibers could, however, not be determined. The nonstriated musclecells of the trabeculae and capsule no doubt also receive their innervation from the nonmedullated nerves (neuraxes of sympathetic neurones).
D. THE BONE-MARROW.
The ingrowing periosteal bud which ushers in the process of endochondral ossification constitutes the first trace of an embryonal bone-marrow (compare p. 117). It consists mainly of elements from the periosteum which penetrate with the vascular bud and later form the entire adult bone-marrow. The red bone-marrow is formed first. This is present in embryos and young animals, and is developed from the above elements during the process of ossification. As Neumann (82) has shown, the red bone-marrow of the human embryo is first formed in the bones of the extremities and gradually replaced in a proximal direction, so that in the adult it is found only in the proximal epiphyses, in the flat bones and in the bodies of the vertebras. In the remaining bones and parts of bones the red bone-marrow is replaced by the yellow bone-marrow (fatmarrow).
As a result of hunger and certain pathologic conditions the yellow bone-marrow changes into a gelatinous substance, which, however, may again assume its original character.
The red bone-marrow, surrounded by a delicate fibrous-tissue membrane, the endosteum, is a tissue consisting of various cellular elements imbedded in a matrix of reticular tissue, which has been demonstrated by Enderlen with the chrome-silver method, and which is similar to the adenoid reticulum. Aside from these cellular elements, the marrow contains numerous vessels (see below), fixed connective-tissue cells, etc.
208
BLOOD AND BLOOD-FORMING ORGANS.
The typical cellular elements of red bone-marrow are: I. The Marrow-cells, or Myelocytes. These are cells, slightly larger than the leucocytes, possessing a relatively large nucleus of round or oval shape, rarely lobular, containing a relatively small amount of chromatin. In the protoplasm of these cells are found (in man) neutrophile granules and now and again small vacuoles. They are said to contain various pigment granules. These cells are not found in normal blood, but are found in circulating blood in certain forms of leukemia, where they may be distinguished from the mononuclear leucocytes partly by their structure, more particu
jT
Fig. 167. Cover-glass preparation from the bone-marrow of dog ; X 1200 (from
preparation of H. F. Miiller) : a, Mast-cell ; b, lymphocyte ; c, eosinophile cell ; d, red
blood-cell ; e, erythroblast in process of division ; f, f, normoblast ; g, erythroblast.
Myelocyte not shown in this figure.
larly by the presence of neutrophile granules not found in the mononuclear leucocytes.
2. Nucleated Red Blood-cells containing Hemoglobin. Two varieties of these cells are recognized structurally, with intermediary stages, as one variety is developed from the other. The erythroblasts, being genetically the earlier cells, possess relatively large nuclei with distinct chromatin network, surrounded by a protoplasm tinged with hemoglobin, and are often found in a stage of mitosis. The other variety of nucleated red blood-cells, the normoblasts, are developed from the erythroblasts. They contain globular nuclei, staining deeply, in which no chromatin network is recognizable, and surrounded by a layer of protoplasm containing hemoglobin. The normoblasts are changed into the nonnucleated red blood-discs by the extrusion of the nucleus. This process occurs normally in the red bone-marrow, or in the venous spaces
THE BONE-MARROW.
2O9
of the bone-marrow (see below). In certain pathologic conditions, nucleated red blood-cells are found in the circulation.
3. Cells with Eosinophile Grannies. In the red bone-marrow are found numerous eosinophile (acidophile) cells, some with round or oval nuclei (mononuclear eosinophile cells), others with horseshoe-shaped nuclei (transitional eosinophile cells), and still others with polymorphous nuclei. The latter, which are the most numerous, are no doubt the mature cells, and are identical with those elements of the blood having the same structure.
/i
"O ' ,^7> 7 %^|
F ^2i ,^;f , O)^
^^<t
Fig. 1 68. From a section through human red bone-marrow ; ^ 680. Technic No. 216 : a, f, Normoblasts ; b, reticulum ; c, mitosis in giant cell ; </, giant cell ; e, h, myelocytes ; g, mitosis ; ;', space containing fat-cells.
4. Cells with basophilic granules. In the bone-marrow are found mononuclear cells in which basophile granules may be differentiated with special reagents.
5. The various forms of leucocytes and the lymphocytes found in blood and lymph.
6. The giant cells (myeloplaxes), which are situated in the center of the marrow, and contain simple or polymorphous nuclei, or lie adjacent to the bone in the form of osteoclasts, which are, as a rule, polynuclear (compare p. 120). The physiologic significance of the giant cells is still obscure. They probably originate from single leucocytes by an increase in size of the latter, and not, as many assume, from a fusing of several leucocytes. The giant cells are endowed with ameboid movement, and often act as phagocytes (the latter quality is denied them by M. Heidenhain, 94).
14
2IO BLOOD AND BLOOD-FORMING ORGANS.
M. Heidenhain (94) has made a particular study of the giant cells. According to him the nuclei of these cells take the form of perforated hollow spheres whose thick walls contain " endoplasm." The latter is continuous with the remaining protoplasm of the cell, the " exoplasm " through the " perforating canals" of the nuclear wall. The exoplasm is arranged in three concentric layers, separated from each other by membranes, the external membrane of the outer zone being the membrane of the cell. The outer layer or marginal zone is of a transient nature, but is always renewed by the cell. Thus, the cell-membrane is replaced by the secondary membrane situated between the second and third zone. According to the same author the functions of the giant cells appear to consist in " the selection and elaboration of certain albuminoid substances of the lymph and blood currents, which are later returned to the circulation." The number of centrosomes occurring in the mononuclear giant cells of the bone-marrow is very large, and in some cases, as in a pluripolar mitosis, may even exceed one hundred in number.
The distribution of the blood-vessels in the bone-marrow is as follows : On entering the bone the nutrient arteries divide into a large number of small branches, which then break up into small arterial capillaries. The latter pass over into relatively large venous capillaries with relatively thin walls, which appear perforated in certain places, so that the venous blood pours into the spaces of the red bone-marrow where the current is very slow. The blood passes out by means of smaller veins formed by the confluence of the capillaries whigh collect the blood from the marrow. It is worth mentioning that the venous vessels, while inside of the bone-marrow, possess no valves ; but, on the other hand, they have an unusually large number of valves immediately after leaving the bone.
Yellow bone-marrow is derived from red bone-marrow by a change of the marrow-cells into fat-cells. The gelatinous marrow, on the contrary, is characterized by the small quantity of fat which it contains. Neither the yellow nor the gelatinous bone-marrow is a blood-forming organ (compare Neumann, 90; Bizzozero, 91 ; H. F. Miiller, 91 ; van der Stricht, 92).
E. THE THYMUS GLAND.
The thymus gland is usually considered as belonging to the lymphoid organs, although in its earliest development it resembles an epithelial, glandular structure. In the epithelial stage, this gland develops from the entoderm of the second and third gill clefts. Mesodermic cells grow into this epithelial structure, proliferate and then differentiate into a tissue resembling adenoid tissue. It retains this structure until about the end of the second year after birth, when it slowly begins to retrograde into a mass of fibrous tissue, adipose tissue, and cellular debris, which structure it presents in adult life.
THE THYMUS GLAND.
21 I
By means of connective-tissue septa, the thymus is divided into larger lobes, and these again into smaller lobes, until finally a number of small, irregularly spheric structures are formed the lobules of the gland. These are, however, connected by cords of lymphoid tissue, the so-called medullary cords. The lobules of the
Fig. 169. A small lobule from the thymus of child, with well-developed cortex,
presenting a structure similar to that of the cortex of a lymph-gland ; X 6 : a,
Hilus ; b, medullary substance ; <r, cortical substance ; d, trabecula.
thymus gland consist of a reticular connective tissue much more delicate at the periphery than at the center of the lobule. The reticulum supports branched connective -tissue cells, with relatively large nuclei. In the meshes of the reticular tissue are cellular elements, in structure similar to the lymphocytes, which are more numerous at the periphery of the lobule than at its center, so that we may here speak of
Fig. 170. Hassal's corpuscle and a small portion of medullary substance, sliowing
reticulum and cells, from thymus of a child ten days old.
the lobule as divided into a cortical and a medullary portion. Leucocytes with polymorphous nuclei, also leucocytes with eosinophile granules, are also found. The medullary portion is usually entirely surrounded by the cortical substance, but may penetrate to the periphery of the lobule, allowing the blood-vessels to enter and
212 BLOOD AND BLOOD-FORMING ORGANS.
leave at this point. In the cortical substance occur changes which result in the formation of structures closely resembling the cortical nodules of lymph-glands.
Until recently, little was known of the significance of this organ. A careful study revealed a similarity between certain cellular elements of the thymus and the constituents of the blood-forming organs, a similarity still more striking from the presence of nucleated red blood-cells in the thymus. Logically, then, the embryonal thymus is to be regarded as one of the blood-forming organs (Schaffer, 93, I).
During embryonic life from the fourth month on and for some time after birth, there are found in the thymus peculiar epithelial bodies, known as the corpuscles of Hassal. They are spheric structures, about o. i mm. in diameter, whose periphery shows a concentric arrangement of the epithelial cells. In their central portions are found a few nuclear and cellular fragments. These bodies occur only in the thymus gland. They are remnants of the primary epithelial, glandular structure of the thymus, and are formed by an ingrowth of mesoderm which breaks down the epithelium into small irregular masses, mechanically compressed by the proliferating mesoderm.
The thymus gland has a relatively rich blood supply. Arterial branches enter the lobules usually near the medullary cords and form capillary networks at the boundaries of the medullary and cortical portions ; from this anastomosing capillaries radiate to the periphery of the lobules, joining to form a relatively dense capillary network under the connective-tissue covering. The veins arise from this capillary network and are situated mostly in the interlobular connective tissue. Certain of the veins are in the medullary portions of the lobules, where they accompany the arteries (Kolliker, v. Ebner).
The lymph-vessels are in the interlobular connective tissue in close apposition with the adenoid tissue.
Nerve-fibers accompanying the blood-vessels have been observed.
II. THE CIRCULATORY SYSTEM
THE walls of the blood-vessels vary in structure in the different divisions of the vascular system. All the vessels, including the heart, possess an inner endothelial lining. In addition to this, the larger vessels are provided with other layers, which consist, on the one hand, of connective and elastic tissue and, on the other, of nonstriated muscle-fibers. The vessels are also richly supplied with nerves, that form plexuses in which ganglion cells are sometimes found, and in the larger vessels the outer layer is honeycombed by nutrient blood-vessels, called vasa vasorum. In the heart, the muscular tissue is especially well developed. According to the structure
THE VASCULAR SYSTEM.
of the vessels, we distinguish, in both arteries and veins, large, medium-sized, small, and precapillary vessels, and finally, the capillaries themselves. The latter connect the arterial and venous precapillary vessels. In the lymphatic system we must further distinguish between the larger lymph-vessels, the sinuses, and the capillaries.
A. THE VASCULAR SYSTEM.
J. THE HEART.
In the heart there are recognized three main coats the endocardium, the myocardium, and the pericardium or epicardium.
The endocardium consists of plate-like endothelial cells, with very irregular outlines. Beneath this endothelial layer is a thin membrane composed of unstriped muscle-cells, together with a small number of connective-tissue and elastic fibers. Below this is a somewhat thicker and looser layer of elastic tissue connected externally with the myocardium. Between the two layers are found, here and there, traces of a layer of Purkinje 1 s fibers (compare p. 147). Purkinje's fibers are found in the heart of many mammalia, although absent in the heart of the human adult.
The auriculoventncular valves of the heart represent, in general, a duplication of the endocardium. The layer of smooth musclefibers found in the latter is better developed on the auricular surface. At the points of insertion of the chordae tendineae the connectivetissue layer is strongly developed and assumes a tendon-like consistency. The semilunar valves of the aorta and pulmonary artery have a similar structure. In the nodules of these valves the elastic fibers are especially dense in their arrangement.
The myocardium is made up of the heart muscle-fibers already described (yid. p. 145). Between the heart muscle- fibers and bundles of such fibers are thin layers of fibrous connective tissue containing a network of capillaries. The myocardium of the auricles may be divided into two layers, of which the outer is common to both auricles, the fibers of which have a nearly circular arrangement, while the deeper layer is separate for each chamber. The arrangement of the heart muscle-fibers of the ventricles is complicated. With special methods of maceration J. B. MacCallum was able to show that "the superficial fibers are found to have origin in the auriculoventricular ring, to wind about the heart spirally, and to end in tendons of the papillary muscle of the opposite ventricle. The deep layers also begin in the tendon of one auriculoventricular ring, pass around to the interventricular septum, cross over backward or forward in this septum, and end in the papillary muscle of the other ventricle. In the light of this, the heart consists of* several bands of muscles with tendons at each end, rolled up like a scroll or like the letter S." The musculature of the auricles is almost completely
214 THE CIRCULATORY SYSTEM.
separated from that of the ventricles by means of the annulus fibrosus atrioventricularis, or the auriculoventricular ring, which consists in the adult of connective tissue containing numerous delicate and densely interwoven elastic fibers.
The pericardium consists of a visceral layer, the epicardium, adhering closely to the myocardium, and a parietal layer (pericardium), loosely surrounding the heart and continuous at the upper portion of the heart with the visceral layer. Between the two layers is the pericardial cavity, containing a small quantity of a serous fluid the pericardial fluid. In the visceral layer (the epicardium) we find a connective-tissue stroma covered by flattened mesothelial cells. A similar structure occurs also in the parietal layer, although here the connective -tissue stroma is considerably reinforced. Deposits of fat, in most cases in the neighborhood of the blood-vessels, are sometimes seen between the myocardium and the visceral layer of the pericardium.
According to Seipp, the distribution of the elastic tissue in the heart is as follows : The endocardium of the ventricles contains far more elastic tissue than that of the auricles, especially in the left ventricle, where even fenestrated membranes may be present. In the myocardium of the ventricles there are no elastic fibers aside from those which are found in the adventitia of the contained bloodvessels. In the myocardium of the auricles, on the contrary, such fibers are very numerous and are continuous with the elastic elements in the walls of the great veins. The epicardium also presents elastic fibers in the auricles continuous with those of the great veins emptying into the heart, and in the ventricles continuous with those in the adventitia of the conus arteriosus. In those portions of the heart-wall containing no muscular tissue the elastic elements of the epicardium are continuous with those of the endocardium. In the new-born the cardiac valves possess no elastic fibers, although they are present in the adult. They are developed on that side of each valve, which, on closing, is the more stretched for instance, on the auricular side of the auriculoventricular valves.
The heart has a rich blood supply. The capillaries of the myocardium are very numerous, and so closely placed around the muscle bundles that each muscular fiber comes in contact with one or more capillaries. In the endocardium the vessels are confined to the connective tissue. The auriculoventricular valves contain blood-vessels, in contradistinction to the semilunar valves, which are non -vascular, while the chordae tendineae are at best very poorly supplied with capillaries.
The coronary arteries, which terminate in the capillaries above mentioned, are terminal arteries in the sense that " the resistance in the anastomosing branches is greater than the blood pressure in the arteries leading to those branches (Pratt, 98). This observer has further shown that the vessels of Thebesius (small veins which open on the endocardial surfaces of the ventricles and auricles and
THE VASCULAR SYSTEM. 21 5
communicate directly with all the chambers of the heart) open from the ventricles and auricles into a system of fine branches that communicate with the coronary arteries and veins by means of capillaries, and with the veins, but not with the arteries, by passages of somewhat larger size"; so that, although the blood supply through the coronary arteries for a given area of the myocardium is cut off, the heart muscle of this area may receive blood through the vessels of Thebesius.
Lymphatic ncttvorks have been shown to exist in the endocardium, and their presence in the pericardium is not difficult to demonstrate. Little is known with regard to the lymph-channels of the myocardium.
The nerve supply of the heart includes numerous medullated nerve-fibers, the dendrites of sensory neurones, and numerous nonmedullated fibers, the neuraxes of sympathetic neurones. Smirnow (95) described sensory nerve-endings in the endocardium of amphibia and mammalia, which he suggests may be the terminations of the depressor nerve. Dogiel (98) has corroborated and extended these observations, and has described complicated sensory telodendria situated both in the endo- and pericardium. The latter states that, after forming plexuses and undergoing repeated division, the medullated sensory nerves lose their medullary sheaths, the neuraxes further dividing in numerous varicose fibers, variously interwoven and terminating in telodendria, which vary greatly in shape and configuration. These telodendria are surrounded by a granular substance containing branched cells, probably connective-tissue cells, the interlacing branches of which form a framework for the telodendria. Similar sensory nerve-endings occur in the adventitia of the arteries and veins of the pericardium (Dogiel, 98) ; and Schemetkin has shown that sensory nerve-endings occur in the adventitia and intima, especially in the latter, of the arch of the aorta and pulmonary arteries. In the heart, under the pericardium on the posterior wall of the auricles and in the sulcus coronarius, are found numerous sympathetic neurones whose cell-bodies are grouped to form sympathetic ganglia. The neuraxes of these sympathetic neurones varicose, nonmedullated nerve-fibers form intricate plexuses situated under the pericardium and, penetrating the myocardium, surround. the bundles of heart muscle-fibers. From the varicose nerve-fibers constituting these plexuses, fine branches are given off, which terminate on the heart muscle-cells in a manner previously described (see p. 166 and Fig. 132). The cell-bodies of the sympathetic neurones, the neuraxes of which thus terminate on the heart muscle-fibers, are surrounded by end-baskets, the telodendria of small medullated nerve-fibers which reach the heart through the vagi. The slowed and otherwise altered action of the heart-muscle, produced on stimulating directly or indirectly the vagus nerves is therefore due not to a direct action of these nervefibers on the heart muscle-cells, but to an altered functional activity
2l6 THE CIRCULATORY SYSTEM.
produced by vagus stimuli in at least some of the sympathetic neurones situated in the heart, the neuraxes of which convey the impulse to the heart muscle. The heart receives further nerve supply through sympathetic neurones, the cell-bodies of which are situated in the inferior cervical and stellate ganglia, the neuraxes of which enter the heart as the augmentor or accelerator nerves of the heart. The mode of ending of these nerve-fibers has not as yet been fully determined. It may be suggested as quite probable that they terminate on the dendrites of sympathetic neurones, the cell-bodies of which are not inclosed by end-baskets of nerves reaching the heart through the vagi, as above described. It is also possible that they end directly on the heart muscle-cells. The cell-bodies of the sympathetic neurones, the neuraxes of which form the augmentor nerves, are surrounded by the telodendria of small medullated fibers, forming end-baskets, which leave the spinal cord through the anterior roots of the upper dorsal nerves. Besides the nerves here described, nonmedullated nerves (whether the neuraxes of sympathetic neurones, the cell-bodies of which are situated inside or outside of the heart has not been fully determined), form plexuses in the walls of the coronary vessels, terminating, it would seem, on the muscle-cells of the media (vasomotor nerves).
2. THE BLOOD-VESSELS.
A cross-section of a blood-vessel shows several coats. The inner consists of flattened endothelial cells, and is common to all vessels. The second varies greatly in thickness, contains most of the contractile elements of the arterial wall, and is known as the media, or tunica media. Its elastic fibers have in general a circular arrangement and are fused at the inner and outer surfaces to form fenestrated membranes, the lamina elastica interna and externa. Outside of the media lies the adventitia or tunica externa, consisting in the arteries almost entirely of connective tissue and in the veins principally of contractile elements, smooth muscle-fibers. Between the internal elastic membrane and the endothelial layer is a fibrous stratum which varies in structure in the different vessels of larger caliber. This is the subendothelial layer, or the inner fibrous layer, and forms, together with the endothelium, the intima or tunica intima. Bonnet (96), as a result of his own investigations, suggests a somewhat different classification of the layers composing the arterial wall. According to him, the endothelium alone constitutes the intima. The elastic membranes, both internal and external, together with the tissue lying between them, and that between the internal elastic membrane and the intima, constitute the media. The tissue layers outside the external elastic membrane form the tunica externa (adventitia).
(a) Arteries. In the great arterial trunks, such as the pulmonalis, carotis, iliaca, etc., the tunica media possesses a very typical
THE VASCULAR SYSTEM. 2 1/
structure. It is divided by means of elastic fibers and membranes
y Intima.
,_ ---- Elastica in.*"> ' terna.
v Endothelium of the intima.
\ Media.
Fenestrated elastic membrane.
Elastica ex terna. Inner layer of
adventitia.
Outer layer of
adventitia. . Vasa vasorum.
Fig. 171. Cross-section of the human carotid artery ; X J 5'
(fenestrated membranes) into a large number of concentric layers containing but few muscle-fibers. Here also the tunica media is separated from the intima by an elastic limiting membrane, the fenestrated membrane of Henle, or the lamina elastica interna. In the aorta this membrane as such is not recognizable. The intima presents three distinct layers the inner composed of flattened endothelial cells, and the other two consisting chiefly of elastic tissue (fibrous layers). Of these latter the inner is the richer in cellular
Endothelium of the
intima. Intima.
Media.
Adventitia with nonstriated muscle-fibers in crosssection.
Fig. 172. Section through human artery, one of the smaller of the medium-sized ; X 640. elements and has a longitudinal arrangement of its fibers, while the
218
THE CIRCULATORY SYSTEM.
Fig. 173. Precapillary vessels from
mesentery of cat : a, Precapillary artery ;
b, precapillary vein possessing no muscular tissue.
outer is the looser in structure, possesses few cellular elements, and shows a circular arrangement of its fibers. The adventitia is also made up of fibre-elastic tissue, but in this case with a still looser structure and a longitudinal arrangement of its elastic fibers. In the outer portion of the adventitia the white fibrous tissue is more abundant. The adventitia is rich i'n blood-vessels.
The medium-sized arteries differ in structure from the larger in
that the elastic elements of the intima and media are replaced to a considerable extent by nonstriated muscular fibers. To this type belong the majority of the arterial vessels, ranging in caliber from the brachial, crural, and radial arteries to the supraorbital artery. In these the intima shows, besides its endothelium, only a single connective-tissue layer with numerous longitudinal fibers, the subendothelial layer, which is thin and is limited externally by the fenestrated membrane of Henle (lamina elastica interna). The media no longer gives the impression of being laminated, but consists of circularly arranged muscle-fibers separated from each other by elastic fibers and membranes and a small amount of fibrous connective tissue in such a way that the muscle-cells form more or less clearly defined groups. Here also the media is limited externally by the external elastic membrane. The adventitia, which becomes looser externally, is not so well developed as in the larger vessels, but presents in general the same structure. In certain arteries (renal, splenic, dorsalis penis) it shows in its inner layers scattered longitudinal muscle-cells, which, however, may also occur in other arteries at their points of division.
With regard to the elastic tissues, the arteries of the brain differ to some extent from those of the remainder of the body. The elastica interna is much more prominent, the elastic fibers in the circular muscular layer are fewer, and the longitudinal strands are almost entirely lacking (H. Triepel).
The walls of the smaller arteries consist mainly of the circular muscular layer of the media. The intima is reduced to the endothelium, which rests directly on the elastic internal limiting membrane. Outside of the external limiting membrane is the adventitia, which now consists of a small quantity of connective tissue. The vasa vasorum have disappeared. To this type belong the supraorbital, central artery of the retina, etc.
In the so-called precapillary vessels the intima consists only of the endothelial layer. The internal elastic membrane is very delicate. The media no longer forms a continuous layer, but is
THE VASCULAR SYSTEM.
219
made up of a few circularly disposed muscular fibers. The adventitia is composed of a small quantity of connective tissue, and contains no vasa vasorum.
(<) Veins. In the foregoing account of the structure of the arteries we have described the structure of their walls according to the caliber of the vessels. Such a differentiation in the case of the veins would be impossible, since sometimes veins of the same caliber present decided differences in structure in various parts of the body.
For the sake of convenience, we will commence with the description of a vein of medium size. Its intima consists of three layers : (i) Of an inner layer of endothelium ; (2) of an underlying layer of muscle-cells, interrupted here and there by connective tissue ; and (3) of a fibrous connective-tissue layer containing fewer elastic but more white fibrous connective -tissue fibers than is the case in the arteries. Externally, the intima is limited by an in
,-'Intima.
T Elastica interna.
Media.
Fenestrated elastic membrane.
Inner layer of the adventitia with
longitudinally arranged musclecells.
Connective tissue of the adventitia.
'".:" ;--V" Nerve.
'
Fig. 174. Cross-section of human internal jugular vein. At the left of the nerve are two large blood-vessels with a smaller one between them (vasa vasorum) ; X I 5 ternal elastic layer. The media is in general less highly developed than that of a corresponding artery, and contains muscle-cells which have a circular arrangement and in some veins form a continuous
22O
THE CIRCULATORY SYSTEM.
layer, although they sometimes occur as isolated fibers. The adventitia shows an inner longitudinal muscular layer, which may be quite prominent and even form the bulk of the muscular tissue in the wall of the vein. Otherwise the adventitia of the veins belonging to this class corresponds in general to that of the arteries of the same size ; but here also we have, as in the intima, a preponderance of white fibrous connective-tissue elements.
In the crural, brachial, and subcutaneous veins, the musculature of the media is prominent ; while in the jugular, subclavian, and innominate veins, and in those of the dura and pia mater, the muscular tissue of the media is entirely wanting, and, as a consequence, the adventitia with its musculature, if present, is joined directly to the intima.
In the smaller veins the vascular wall is reduced to an endothelial lining, an internal elastic membrane, a media consisting of interrupted circular bands of smooth muscle-fibers (which may be absent), and an adventitia containing a few muscle-fibers. The precapillary veins, which possess in general thinner walls than the corresponding arteries, present a greatly reduced intima and adventitia, while the media has completely disappeared.
Adventitia with
nonstriated
muscle-cells
in cross-sections.
Fig- 175- Section of small vein (human); X 640.
The valves of the veins are reduplications of the intima and vary slightly in structure at their two surfaces. The inner surface next to the blood current is covered by elongated endothelial cells, while the outer surface possesses an endothelial lining composed of much shorter cellular elements. The greater part of the valvular structure consists of white fibrous connective-tissue and elastic fibers. Flattened and circularly arranged muscle-cells are met with at the inner surface of many of the larger valves. The elastic fibers are more numerous beneath the endothelium on the inner surface of the valves (Ranvier, 89).
(r) The Capillaries. The capillaries consist solely of a layer of endothelial cells, accompanied here and there by a very delicate structureless membrane, and rarely by stellate connective-tissue cells. The connective tissue in the immediate neighborhood of the capillaries is modified to such an extent that its elements, especially those of a cellular nature, seem to be arranged in a direction parallel with the long axis of the capillaries. When examined in suitable prepara
THE VASCULAR SYSTEM.
221
tions, the endothelium of the capillaries is seen to form a continuous layer, the cells of which are, as a rule, greatly flattened and present very irregular outlines.
It is a well-known fact that a migration of the leucocytes occurs from the capillaries and smaller vessels (compare p. 193). In this connection arises the question as to whether or not the cells pass through certain preformed openings in the endothelium of these vessels, the so-called stomata, or through the stigmata and intercellular cement uniting the endothelial cells. The latter seems more probable, as stomata do not occur normally in the capillary wall. This subject will be further touched upon in the description of the lymphatic system.
The capillaries connect the arterial and venous precapillary vessels, and in general accommodate themselves to the shape of the elements of tissues or organs in which they are situated. In the
Fig. 176. Endothelial cells of capillary (a) and precapillary (b) from the mesentery of
rabbit ; stained in silver nitrate.
muscles and nerves, etc., they form a network with oblong meshes, while in structures having a considerable surface, such as the pulmonary alveoli, the meshes are more inclined to be round or oval ; such small evaginations of tissue as the papillae of the skin contain capillaries arranged in the shape of loops. In certain organs as, for instance, in the lobules of the liver the capillaries form a distinct network with small meshes.
Sinusoids. In connection with the description of capillaries we may here insert a brief account of another type of terminal or peripheral blood-channels, described by Minot under the name of sinusoids; his account is here followed. The sinusoids are also composed only of endothelial cells. They differ, however, from blood-capillaries in shape and size, in their relation to the cellular elements of the tissues in which they are found, and in their development. They are of relatively large size, and vary between wide extremes. They are of very irregular shape and anastomose freely. "A sinusoid has its endothelium closely fitted against the paren
222
THE CIRCULATORY SYSTEM.
chyma of the organ," without the intervention of connective tissue; or, when this is present, usually only in small quantity, it is secondarily acquired, since in the early developmental stages of sinusoids no connective tissue intervenes between them and the parenchyma of the tissue. They develop by the intergrowth and intercrescence of the parenchyma of the organ and venous endothelium. Sinusoids are found in the following organs : liver, suprarenal, heart, parathyroid, carotid gland, spleen, and hemolymph glands.
(d] Anastomoses, Retia mirabilia, and Sinuses. In the course of certain vessels, abrupt changes are seen to occur as, for instance, when a small vessel suddenly breaks up into a network of capillary or precapillary vessels, which, after continuing as such for a short distance, again unite to form a larger blood-channel, the latter then dividing as usual into true capillaries. Such structures are known as retia mirabilia, and occur in man in the kid Sensory nerve-ending.
Plexus of vasomotor nerves.
r
Fig. 177. Small artery from the oral submucosa of cat, stained in methyleneblue, and showing a small portion of a sensory nerve-ending and the plexus of vasomotor
ney, intestine, etc. Again, instead of breaking up into capillaries, a vessel may empty into a large cavity lined by endothelial cells (blood sinus). The latter is usually surrounded by loose connective tissue and is capable of great distention when filled with blood from an afferent vessel, or when the lumen of the efferent vessel is contracted by pressure or otherwise. The cavernous or erectile tissue of certain organs is due to the presence of such sinuses (penis, nasal mucous membrane, etc.). If vessels of larger caliber possess numerous direct communications, a vascular plexus is the result ; but if such communications occur at only a few points, we speak of anastomoses. Especially important are the direct communications between arteries and veins without the mediation of capillaries. Certain structural conditions of the tissue appear to favor such anomalies, which occur in certain exposed
THE LYMPHATIC SYSTEM. 223
areas of the skin (ear, tip of nose, toes) and in the meninges, kidney, etc.
The blood-vessels, and more particularly the arteries, possess a rich nerve supply, comprising both nonmedullated and medullated nerves. The nonmedullated nerves, the neuraxes of sympathetic neurones, the cell-bodies of which are situated as a veiy general rule in some distant ganglion, form plexuses in the adventitia of the vessel-walls ; from this, single nerve-fibers, or small bundles of such, are given off, which enter the media and, after repeated division, end on the involuntary muscle-cells in a manner previously described. (See p. 166 and Fig. 133.) Through the agency of these nerves, the caliber of the vessel is controlled. They are known as vasomotor nerves. Quite recently Dogiel, Schemetkin, and Huber have shown that many vessels possess also sensory nerve-endings. The medullated nerve-fibers terminating in such endings, branch repeatedly before losing their medullary sheaths. These nerve-fibers with their branches accompany the vessels in the fibrous tissue immediately surrounding the adventitia. The nonmedullated terminal branches end in telodendria, consisting of small fibrils, beset with large varicosities and usually terminating in relatively large nodules.
The branches and telodendria of a single medullated nerve-fiber (sensory nerve) terminating in a vessel are often spread over a relatively large area, some of the branches of such a nerve often accompanying an arterial branch, to terminate thereon. In the large vessels, the telodendria of the sensory nerves ajre found not only in the adventitia, but also in the intima, as has been shown by Schemetkin. (Seep. 215.)
B. THE LYMPHATIC SYSTEM.
\. LYMPH-VESSELS.
The larger lymph-vessels the thoracic duct, the lymphatic trunks, and the lymph-vessels have relatively thin walls, and their structure corresponds in general to that of the veins. They possess numerous valves, and are subject to great variation in caliber according to the amount of their contents. When empty, they collapse and the smaller ones are not easily distinguished from the surrounding connective tissue. Tiraofeew and Dogiel (97) have shown that the lymph -vessels are supplied with nerves, which in their arrangement are similar to those found in the arteries and veins, though not so numerous. The latter, who has given the fuller description, states that the nerves supplying the lymphvessels are varicose, nonmedullated fibers which form plexuses surrounding these structures. The terminal branches would appear to end on the nonstriated muscle cells found in the wall of the lymph -vessel.
224 THE CIRCULATORY SYSTEM.
2. LYMPH CAPILLARIES, LYMPH-SPACES, AND SEROUS CAVITIES.
The walls of the lymph capillaries consist of very delicate, flattened endothelial cells, which are, however, somewhat larger and more irregular in outline than those of the vascular capillaries. The two may also be further differentiated by the fact that the diameter of the lymph capillaries varies greatly within very short distances. From a morphologic standpoint, the relations of the lymph capillaries to the vascular capillaries and adjacent tissues are among the most difficult to solve. The distribution of the lymph-vessels and capillaries can be studied only in injected preparations, and it is easily seen that structures of such elasticity and delicacy are peculiarly liable to injury by bursting under this method of treatment. The resulting extravasations of the injection-mass then spread out in the direction of least resistance and still further obscure the picture, rendering it difficult to determine what spaces are preformed and what are the result of the injection. So much is, however, certain : that the more carefully and skilfully the injection is made, the greater are the areas obtained, showing the injection of true lymph capillaries. The recent work of W. G. MacCallum confirms this, since he has shown quite conclusively that the lymphatics form a system of channels, with continuous walls, and are thus not in direct communication with the so-called intercellular lymph-spaces the lymphcanalicular spaces. Further confirmation of the fact that the lymphatics form a closed system of channels is found in the excellent contribution of Dr. Florence R. Sabin, dealing with the development of the lymphatic system. It is here shown that the lymphatic system begins as two blind ducts, guarded by valves, which bud off from the veins of the neck, and from two similar buds which arise from veins in the inguinal region. These buds grow and enlarge to form lymph-hearts, and from these ducts grow out toward the skin, which they invade and in which they spread out to form anastomosing plexuses. Ducts also grow toward the aorta to form the anlagen for the thoracic ducts, and from these grow out and invade the various organs.
In some regions very dense networks of lymph capillaries surrounding the smaller blood-vessels have been demonstrated. Larger cleft-like spaces, lined with endothelium and communicating with the lymphatic system, are also found surrounding the vessels, perivascular spaces. These are present in man in the Haversian canals of bone tissue, around the vessels of the central nervous system, etc., and are separated from the actual vessel-wall by flattened endothelial cells. As in the case of the so-called perilympJiatic spaces, the walls of the perivascular spaces are joined here and there by connective-tissue trabeculae covered by endothelium. Such structures exist in the perilymphatic spaces of the ear, the subdural spaces of the pia, the subarachnoidal space, the lymph-sinuses, etc. The perivascular spaces are better developed in the lower animals (amphibia, reptilia, etc.) than in mammalia.
THE CAROTID GLAND.
225
Mention has been made of the migration of leucocytes and, under certain conditions, of red blood-cells through the walls of blood capillaries, and in the case of the former through the walls of lymph capillaries and lymph-vessels and spaces. This diapedesis of leucocytes probably takes place by a wandering of these cells through the intercellular cement uniting the endothelial cells lining these spaces. According to later investigations, it would seem that leucocytes may bore through endothelial cells, and thus migrate from the vessel or space in which they are found previous to such migration.
C THE CAROTID GLAND (GLANDULA CAROTICA, GLOMUS CAROTICUM).
At the point where the common carotid divides, there lies in man a small oval structure about the size of a grain of wheat, known as the carotid gland or the glomus caroticum. It is imbedded in
^ Septum.
Trabecula of
cells in crosssection.
Distended blood capillaries.
_. Efferent vein.
Fig. 178. Section of a cell-ball from the glomus caroticum of man ; X I ^- (Injected specimen, after Schaper.)
connective tissue, surrounded by many nerve-fibers, and on account of its great vascularity has a decidedly red color. The connectivetissue envelope of the gland penetrates into the interior in the form of septa, which divide its substance into small lobules, and these in turn into smaller round masses, the cell-balls. A small branch from the internal or external carotid enters the gland, where it branches, sending off twigs to the lobules, and these in turn still 15
226 THE CIRCULATORY SYSTEM.
smaller divisions to the cell-balls. The latter vessels break up into capillaries, which merge at the periphery of each cell-ball to form a small vein, from which the larger trunks that pass from the lobules are derived. Each lobule is thus surrounded by a venous plexus from which the larger veins originate that leave the organ at several points. The cell-balls are composed of cellular cords, or trabeculae, the elements of which are extremely sensitive to the action of reagents. The cells are round or irregularly polygonal and separated from each other by a scanty reticular connective tissue. The capillaries already mentioned come in direct contact with the cells of the cell-balls. The organ contains a relatively large number of nerve-fibers and a few ganglion cells.
As the individual grows older, the organ undergoes changes which finally make it unrecognizable. The former belief that the carotid gland was developed as an evagination of one of the visceral pouches has been replaced by a newer theory which gives it an origin solely from the vessel-wall (vid. Schaper). The structure of the coccygeal gland is in general like that of the carotid gland here described.
TECHNIC (BLOOD AND BLOOD-FORMING ORGANS).
Red blood-corpuscles may be examined in the blood fluid without special preparation. . The tip of the finger is punctured and a small drop of blood pressed out, placed upon a slide, and immediately covered with a cover-glass and examined. In such preparations the red bloodcells soon become crenated. The evaporation causing the crenation may be prevented by surrounding the cover-glass with oil (olive oil). A fluid having but slight effect upon the red blood-cells is Hayem's solution, which, however, is not adapted to the examination of leucocytes. It consists of sodium chlorid i gm., sulphate of soda 5 gm., corrosive sublimate 0.5 gm., and water 200 gm. The fresh blood is brought directly into this solution, the amount of which should be at least one hundred times the volume of the blood to be examined. The fixed blood-cells sink to the bottom, and after twenty-four hours the fluid is carefully poured off and replaced by water. The blood-corpuscles are then removed with a pipet and examined in dilute glycerin. They may be stained with eosin and hematoxylin.
Fresh red blood-corpuscles may also be fixed in osmic acid and other special fixing agents. This is done by dropping a small quantity of blood into the fixing fluid ; the blood-cells immediately sink and allow the osmic acid to be decanted ; they are then washed with water, drawn up with a pipet, and examined in dilute glycerin.
Cover-glass Preparations. A method almost universally used consists in preserving the blood-corpuscles in dry preparations. A drop of fresh blood is placed between two thoroughly cleaned cover-glasses, which are then quickly drawn apart, leaving on the surface of each a thin film of blood which dries in a few moments at ordinary room temperature. The specimens are further dried for several hours at a temperature of 120 C. After they have been subjected to this process, they may be stained, etc. The same results may be obtained by treating specimens dried in the air
TECHNIC (BLOOD AND BLOOD-FORMING ORGANS). 227
with a solution of equal parts of alcohol and ether for from one to twentyfour hours, after which they are again dried in the air, and are then ready for further treatment.
A cover-glass preparation of fresh blood may also be treated for a quarter of an hour with a concentrated solution of corrosive sublimate in saline solution, then washed with water, stained, dehydrated with alcohol and mounted in Canada balsam. A concentrated aqueous solution of picric acid may also be used, but in this case the specimen should remain in it for from twelve to twenty-four hours.
The elements of the blood may also be examined in sections. Small vessels are ligated at both ends, removed, fixed with osmic acid, corrosive sublimate, or picric acid, and imbedded in paraffin.
After fixation by any of the above methods the blood-cells may be stained. Eosin brings out very well the hemoglobin in the bloodcells, coloring it a brilliant red ; the stain should be used in very dilute aqueous or alcoholic solutions (i% or less), or in combination with alum (eosin i gm., alum i gm., and absolute alcohol 200 c.c., E. Fischer). Eosin may also be used as a counterstain subsequent to a nuclear stain for instance, hematoxyiin. The preparation is stained for about ten minutes, then washed in water or placed in alcohol until the blood-cells alone remain colored ; the cover-glass preparation should then be thoroughly dried between filter-paper and mounted in Canada balsam. Besides eosin, other acid stains as orange G, indulin, and nigrosin have the property of coloring blood-cells containing hemoglobin.
Blood platelets are best fixed with osmic acid, and may be seen without staining. They may also be stained and preserved in a sodium chlorid solution to which methyl-violet is added in a proportion of i : 20000 (Bizzozero, 82). Afanassiew adds 0.6% of dry peptone to the solution (this fluid must be sterilized before using).
Ehrlich's Granulations. The leucocytes of the circulating blood and those found in certain organs possess granulations which were first studied by Ehrlich and his pupils, and which may be demonstrated by certain methods. The names given to these granulations are based upon Ehrlich's classification of the anilin stains, which differs from that of the chemist. This author distinguishes acid, basic, and neutral stains. By the acid stains he understands those combinations in which the acid is the active staining principle, as in the case of the picrate of ammonia. Among these are congo, eosin, orange G, indulin, and nigrosin. The basic stains are those which, like the acetate of rosanilin, consist of a color base and an indifferent acid. To these belong fuchsin, Bismarck brown, safranin, gentian, dahlia, methyl-violet, methylene-blue, and toluidin. Finally, the neutral anilins may be considered as those stains which, like the picrate of rosanilin, are formed by the union of a color base with a color acid. The granula may be demonstrated in dry preparations as well as in those fixed with alcohol, corrosive sublimate, glacial acetic acid, and sometimes even Flemming's solution. Five kinds of granules are distinguished, and designated by the Greek letters from alpha to epsilon.
The a-granules (acidophile, eosinophile) occur in leucocytes of the normal blood, in the lymph, and in the tissues, and are differentiated from the others by their peculiar staining reaction to all acid stains. They are first treated for some hours with a saturated solution of an acid
228 THE CIRCULATORY SYSTEM.
stain (preferably eosin) in glycerin, washed with water, subsequently colored with a nuclear stain (as hernatoxylin or methylene-blue), and then dried and mounted in Canada balsam. Sections may be treated in the same way, with the exception that after being washed with water, they are first dehydrated with absolute alcohol before mounting in balsam. Another method by which both nuclei and granules are stained consists in the use of Ehrlich's hernatoxylin solution (see page 43), to which 0.5% eosin is added. Before using, the. solution should be permitted to stand exposed to the light for three weeks. This mixture stains in a few hours, after which the preparation is washed with water, treated with alcohol, and then mounted in Canada balsam. The a-granules appear red, the nuclei blue.
The /3-granules (amphophile, indulinophile) stain as well in acid as in basic anilins. They do not occur in man, but may be observed in the blood of guinea-pigs, fowl, rabbits, etc. They are demonstrated as follows : Equal parts of saturated glycerin solutions of eosin, naphthylamin-yellow, and indulin are mixed, and the dried preparations treated with this combination for a few hours, then washed with water, dried between filter-paper, and mounted in Canada balsam. The amphophile granules are stained black, the eosinophile granules red, the nuclei black, and the hemoglobin yellow.
The T' -granules, or those of the mast-cells, are found in normal tissues and also in small quantities in normal blood, and are found in larger numbers in leukemic blood. They may be shown by two methods : (i) A mixture is made consisting of concentrated solution of dahlia in glacial acetic acid 12.5 c.c., absolute alcohol 50 c.c. , distilled water 100 c.c. (Ehrlich). The treatment is the same as for the amphophile granules ; (2) Westphal's alum-carmin-dahlia solution (vid. Ehrlich). This mixture is used in staining dry preparations as well as sections of objects fixed for at least one week in alcohol. Alum i gm. is dissolved in distilled water 100 c.c., and carmin i gm. added. The whole is then boiled for one-quarter hour, cooled, filtered, and 0.5 c.c. of carbolic acid added (Grenacher's alum-carmin, see page 42). This solution is now mixed with 100 c.c. of a saturated solution of dahlia in absolute alcohol, glycerin 50 c.c., and glacial acetic acid 10 c.c., the whole stirred and allowed to stand for a time. The specimen is stained for twenty-four hours, decolorized in absolute alcohol for the same length of time, and finally mounted in Canada balsam. The ^-granules are colored a dark blue and the nuclei red. A simpler method of demonstrating the ^-granules consists in overstating dry and fixed cover-glass preparations with a saturated aqueous solution of methylene-blue, decolorizing for some time in absolute alcohol, drying between filter-papers, and mounting in Canada balsam.
The ^-granules (basophile) occur in mononuclear leucocytes of the human blood. Their staining may be accomplished in a few minutes by treating fixed cover-glass preparations with a concentrated aqueous solution of methylene-blue, after which they are washed with water, dried between filter-papers, and mounted in Canada balsam.
The e- or neutrophile granules which are found normally in the polynuclear leucocytes of man (as also in pus-cells), in some of the transitional cells, and in the myelocytes, are stained by Ehrlich as follows : 5 vols. of a saturated aqueous solution of acid fuchsin are mixed with i vol.
TECHNIC (BLOOD AND BLOOD-FORMING ORGANS). 229
of a concentrated aqueous solution of methylene-blue. To this 5 vols. of water are added, and the whole allowed to stand for a few days, after which the solution is filtered. This mixture stains in five minutes, and the specimen is then washed with water, etc. The neutrophile granules are colored green, the eosinophile granules red and the hemoglobin yellow.
Neutrophile and eosinophile granules may also be stained in Ehrlich's neutrophile mixture :
Orange G, saturated aqueous solution, . . 130 to 135 c.c. Acid fuchsin, " " " . . 80 to 120
Methyl-green, " " " . . 125
Distilled water, 300
Absolute alcohol, 200
Glycerin, loo
Mix the above quantities of orange G, acid fuchsin, water, and alcohol in a bottle and add slowly, while shaking the bottle, the methyl-green and finally the glycerin. The cover-glass preparations should be fixed in the ether and alcohol solution for about one hour, or fixed with dry heat at a temperature of noC. for from fifteen to thirty minutes. Float the preparation on a small quantity of the stain for about fifteen minutes, wash in water, dry and mount in balsam. The red blood-cells are stained a reddish -brown color (brick-color), all nuclei a light blue-gieen, the eosinophile granules a fuchsin-red, and the neutrophile granules a violetred. Griibler, of Leipzig, has prepared a dry powder, known as the Ehrlich-Biondi-Heidenhain three-color mixture, which is prepared for use by making a 0.4% solution in distilled water, to 100 c.c. of which are added 7 c.c. of a 0.5% aqueous solution of acid fuchsin.
Wright's Method of Staining Blood Films. This excellent and rapid method is especially recommended.
Stain. Make a one-half per cent, aqueous solution of sodium bicarbonate in an Erlenmeyer flask and add to it one per cent, of methyleneblue. Steam for one hour in an Arnold steam sterilizer and allow mixture to cool, and when it is cold pour in a large dish. To 100 c.c. of this solution add about 500 c.c. of a one-tenth per cent, aqueous solution of eosin (Grubler's yellowish eosin, soluble in water). The quantity of the eosin solution can not be definitely given ; it is added while constantly stirring until the solution becomes of purple color and a yellowish scum with metallic luster forms on the surface and a finely granular black precipitate appears in suspension. The precipitate is collected on a filter and allowed to dry thoroughly. Make a saturated solution in pure methylic alcohol (0.3 gm. of precipitate to 100 c.c. of methylic alcohol) and filter. To 80 c.c. of the filtrate 20 c.c. of methylic alcohol is added to complete the stain.
Staining of Blood Films. Allow blood film to dry in the air and pour as much of the stain on the cover-glass or slide as it will hold, allowing it to remain in contact with the preparation for about one minute ; then add, drop by drop, enough water to make the stain semitransparent, and a reddish tinge appears at the borders and a metallic scum on the surface. This diluted stain remains on the preparation two or three minutes. The preparation is now washed in distilled water until the better parts have a yellowish or reddish color. Dry quickly between filter-papers and mount on balsam. Red cells are orange or
23O THE CIRCULATORY SYSTEM.
pink in color ; the nuclei, of blue color of varying intensity, eosinophile granules red, neutrophile granules reddish- lilac, basophile granules dark blue or almost black.
The hemoglobin shows itself in the form of crystals. In certain teleosts the crystals are formed in the blood-corpuscles around the nuclei and often within a short time after death. In old alcoholic specimens, hemoglobi"n crystals (blood crystals) are found in the vessels and were first discovered here by Reichert in the blood of the guinea-pig. They have been found in large quantities in the splenic blood of a sturgeon which had been preserved for forty years in alcohol. The hemoglobin crystals belong to the rhombic series of crystallographic classification. The simplest method of demonstrating hemoglobin crystals is probably the following : The blood is first defibrinated by whipping or agitating with mercury, after which process sulphuric ether is added, drop by drop, until the mixture has been made laky ; this change may be detected macroscopically by the sudden change from an opaque to a dark, transparent, cherry-red color. No red blood-cells should now be seen under the microscope. The preparation is placed on ice for from twelve to twenty-four hours after which a drop of the blood is placed on a slide. In half an hour it will be seen that the margin of the drop has begun to dry. A cover-slip is now applied and, after a few minutes, numerous crystals are seen to form at the margin of the drop, a process which may be followed under the microscope. Large hemoglobin crystals are obtained by Gscheidtlen as follows : Defibrinated blood is placed in a glass tube, which is then hermetically sealed. The blood is now subjected to a temperature of about 40 C. for two or three days ; if then the glass be broken and the blood poured into a flat dish, large hemoglobin crystals are immediately formed. Crystals also appear if a drop of laky blood be placed in a thick solution of Canada balsam in chloroform and covered with a cover-slip.
Hemin crystals (Teichmann's crystals ; hemin is hematin-chlorid) in the shape of rhombic plates are very easily obtained from the blood. A drop of the latter is placed on a slide and carefully mixed with a small drop of normal salt solution. This is then carefully warmed until the fluid evaporates and leaves a reddish-brown residue, after which a coverglass is applied and glacial acetic acid added until the space between slide and cover-glass is filled. The preparation is now heated until the acetic acid boils. As soon as the latter evaporates, Canada balsam may be brought under the cover-glass, thus producing a permanent specimen. When fluids or stains suspected of containing blood are to be examined, the hemin crystals become of the utmost importance, as their demonstration is then a positive indication of the presence of blood. Fluids are evaporated and treated with glacial acetic acid as above directed. Suspected blood stains on cloth are treated as follows : Small pieces are cut from the cloth in the region of the stain, soaked in normal salt solution, and the resulting fluid treated as above. If the stain is on wood or other solid object, the stain is scraped off and dissolved in normal salt and then tested for hemin crystals. Hemin crystals are almost or entirely insoluble in water, alcohol, ether, ammonia, glacial acetic acid, dilute sulphuric acid, and nitric acid. They are, however, soluble in potassium hydrate.
A third form of crystals occasionally found in the blood and frequently in the corpora lutea and, under pathologic conditions, also in apo
TECHNIC (BLOOD AND BLOOD-FORMING ORGANS). 231
plectic areas, are the hematoidin crystals first discovered by Virchow. Masses of these crystals have an orange color. Microscopically, they appear as red rhombic plates. As they are soluble in neither alcohol nor chloroform, they are easily preserved in Canada balsam. Their artificial production has as yet never been accomplished. Hematoidin contains no iron.
The fibrin thrown down when the blood coagulates may be demonstrated upon the slide in the form of very fine particles and filaments. A drop of blood is brought upon the slide and kept for a time in a moist chamber or on the table until it begins to clot ; after which a cover-slip is applied and the preparation washed with water by continued irrigation. In this manner most of the red blood-corpuscles are removed. Lugol solution may now be added, which stains brown the filaments of the fibrin network adherent to the slide. In order to see the fibrin network in sections, it is better to use specimens previously fixed in alcohol ; the sections are stained for ten minutes in a concentrated solution of gentian-violet in anilin water (Weigert), rinsed in normal salt solution, treated for about ten minutes with iodo-iodid of potassium solution, and then spread upon a slide and dried with filter-paper. They are now placed in a solution consisting of 2 parts of anilin oil and i part of xylol until they become perfectly transparent. This solution is then replaced by pure xylol and finally by Canada balsam. The fibrin network is stained a deep violet.
Blood Current. There are different methods and a variety of material at our disposal for the demonstration of the blood current through the vessels. The best object for this purpose is probably the frog. The procedure is as follows : The animal is immobilized by poisoning with curare. ^ gm. of a i % aqueous solution injected into the dorsal lymph-sac will immobilize the frog in a short time. The exact dose can not, however, be given, as the commercial curare is not a uniform chemical compound ; the dose must therefore be ascertained by experiment. As is well known, curare affects exclusively the nerve end-organs of striated voluntary muscle, but does not affect either the heart muscle or unstriated muscular tissue ; hence the utility of curare for this purpose. In order to see the blood current, it is only necessary to stretch the transparent web between the frog's toes and fasten it with insect needles to a cork plate having a suitable opening. If the cork plate be large enough to accommodate the whole frog, it may be placed in such a position that its opening lies over that in the stage of the microscope. The web thus spread out may be examined with a medium magnification. The tongue of the frog is also used for the same purpose. As the latter is attached to the anterior angle of the lower jaw, it may be conveniently drawn out, suitably stretched, and then placed over the hole in the cork plate. A very good view of the circulation may be obtained by examining the mesentery of a frog. The migration of the leucocytes through the vessel-walls can also be studied in such preparations. An incision 0.5 cm. in length is made in the right axillary line through the skin of a frog (best in the male), care being taken not to injure any vessels (which can be seen through the skin in frogs possessing little pigment). The abdominal muscles are then incised and a pair of forceps introduced to grasp one of the presenting intestinal loops. The latter is then attached to the cork plate with needles, and the mesentery carefully stretched over the opening. On examining the specimen it is best to moisten it with normal salt solution and to cover the area to be
232
THE CIRCULATORY SYSTEM.
examined with a fragment of a cover-glass. The lung may also be examined, but here the incision must be farther forward.
Counting Blood=cells. The instrument now generally used for this purpose is the Thoma-Zeiss hemocytometer. This apparatus consists of two parts : pipettes by means of which the blood is diluted 100 times, when counting red, or 10 times when white blood-cells are to be counted, and a glass slide, on which there is a small well of known depth, the bottom of the well being divided off into small squares. The pipette used when counting the red cells consists of a capillary tube, near the middle of which there is an ampullar enlargement. This is so graduated that the cubical contents of the capillary tube is just one-hundredth part of the cubical contents of the ampulla. The blood to be examined is drawn into the capillary tube to a line marked i (just below the ampulla); the end of the pipette is then inserted into the diluting fluid, and this is sucked up until the diluted blood reaches a line marked 101 (just above
Fig. 179. Thoma-Zeiss hemocytometer: a, Slide used in counting ; b, sectional view ;
f, a portion of ruled bottom of the well ; </, pipette.
the ampulla). The pipette is then carefully shaken to mix thoroughly the blood and the diluting fluid.
Either of the following two solutions may be used for diluting the blood :
Hay em ' s Solution :
Bichlorid of mercury o. 5 gm.
Sodium chlorid j .o gm.
Sodium sulphate 5.0 gm.
Distilled water 200.0 c.c.
Toisori 1 s Fluid (as given by V. Kahlderi) :
Methyl violet 58 0.025 gm.
Neutral glycerin 30.0 c.c.
Distilled water 80.0 c.c.
Mix the methyl violet with the glycerin and distilled water ; to this solution is added
Sodium chlorid (C. P. ) l.o gm.
Sodium sulphate (C. P.) 8.0 gm.
Distilled water 80.0 c.c.
TECHNIC (BLOOD AND BLOOD-FORMING ORGANS). 233
Filter, and the solution will be ready for use. The white blood-cells are stained violet, and may thus be counted with the red.
The diluting fluid contained in the capillary tube is then blown out, and a small drop of the diluted blood is placed on the center of the small glass disc. The small disc is surrounded by a ring of glass, cemented to the slide. This glass ring is o.i mm. thicker than the glass disc. When this small chamber is covered with a thick cover-glass, we have a layer of blood o. i mm. deep between the disc and the cover-glass. On the upper surface of the small glass disc (on which the drop of diluted blood was placed) there are marked off 400 small squares. The sides of the small squares are ^V rnm. long. It will be seen that the layer of blood over each of the squares would have a cubical contents of
?oW of a cubic millimeter (^ X io X TO = 3^0 <y) The hemocytometer slide is now placed on the stage of the microscope, where it should remain undisturbed for several minutes before counting. The red blood-cells in 25 to 50 squares are then counted. To ascertain the number of red cells in a cubic millimeter the following formula may be useful :
(each mass of") ( ,., .. ") - f j n 1 f
blood counted, 1 Xd \ t^' [ X" \ S F rtWc.mm. j l hereICO J l counted j I number of red
n (number of squares counted) ; 1 blood-cells in
1 I c.nim.
Or, ascertain the average of the red blood-cells in the squares counted, and multiply this number by 400,000.
In case it is desired to count only the white blood-corpuscles, a ^ per cent, solution of glacial acetic acid is used for diluting the blood. This solution bleaches the red cells, and brings out clearly the white corpuscles. The blood is diluted only ten times, using for this purpose the ThomaZeiss pipette for counting white corpuscles. The formula then reads as follows :
( the number of white "| 4000 X d(io) X n \ blood - corpuscles >
( counted. J the number of white
= blood-cells found in
n (number of squares counted). a cubic millimeter.
Or, multiply the average number of white corpuscles in each square by 40,000.
Lymph-glands. To obtain a general idea of the structure of lymphatic glands, sections are made of small glands fixed in alcohol or corrosive sublimate. They are then stained with hematoxylin and eosin. In such preparations the cortical and medullary substances can be studied ; the trabeculae and blood take the eosin stain.
The flattened endothelial cells covering the trabeculae are brought to view by injecting a o. i% solution of silver nitrate into a fresh lymphatic gland. After half an hour the gland is fixed with alcohol and carried through in the regular way ; the sections should be quite thick (not under 20 //). After the sections have been mounted in Canada balsam and exposed to light for a short time, the endothelial mosaic will be seen wherever the silver nitrate has penetrated.
234 THE CIRCULATORY SYSTEM.
Fixing with Flemming's solution and staining with safranin is the best method for studying the germ centers of the lymph-follicles. Other fluids which bring out the mitoses may also be employed.
Reticular tissue is best demonstrated by sectioning a fresh gland with a freezing microtome, removing a section to a test-tube one-quarter filled with water, and agitating it. The lymphocytes are thus shaken out of the meshes of the reticulum, leaving the latter free for examination.
The same results can be obtained by placing a section prepared in the above-named manner upon a slide, wetting it with water, and carefully going over it with a camel's-hair brush. The lymphocytes adhere to the brush. Both methods (His, 61) may be applied to hardened sections which have lain in water for a day or so. In this case, however, the removal of the lymphocytes is not so easy as in fresh sections.
In thick sections the reticulum is hidden by the lymphocytes. If, on the other hand, very thin sections (not over 3 /*) be made, especially of objects fixed in Flemming's solution, the adenoid reticulum stands out clearly without any further manipulation.
The reticular structure may also be demonstrated by an artificial digestion of the sections with trypsin. The sections are then agitated in water, spread on a slide, dried, then moistened with a picric acid solution (i gm. in 15 c.c. of alcohol and 30 c.c. of water), again dried, covered with a few drops of fuchsin S solution (fuchsin S i gm., alcohol 33 c.c., water 66 c.c.), and left to stand for half an hour. The fuchsin solution is then carefully removed, the section washed again for a short time in the same picric acid solution, then treated with absolute alcohol, xylol, and finally mounted in Canada balsam. The reticular tissue of both lymphatic glands and spleen are stained a beautiful red (F. P. Mall). (See also page 129.)
The treatment of splenic tissue is practically the same as that of the lymphatic glands.
In all these organs (lymph-glands, spleen, and bone-marrow) a certain amount of fluid may be obtained by scraping the surface of the fresh tissue. This may then be examined in the same manner as blood and lymph (see Technic of same). Sections of lymph -glands and spleen previously fixed in alcohol, mercuric chlorid, or even in Flemming's solution may be examined by the granula methods of Ehrlich.
By using the chrome-silver method a peculiar network of reticular fibers may be seen in the spleen. (Gitterfasern ; Oppel, 91.)
The examination of the bone=marrow belongs also to this chapter. The marrow of the diaphysis is taken out by splitting the bone longitudinally with a chisel. With a little practice, it is easy to obtain small pieces of the marrow, which are then fixed by the customary methods and cut into sections. In the epiphysis the examination is confined either to the pressing out of a small quantity of fluid with a vice, or to the decalcification of small masses of spongy bone, containing red bone-marrow. In the first case, methods applicable to blood examination are employed ; in the second, section methods (see also the petrification method, page 132) are used. The methods given for the preparation of lymph -glands and spleen are also applicable in many cases.
THE ORAL CAVITY. 235
TECHNIC (CIRCULATORY SYSTEM).
To obtain a topographical view of the layers composing the heart and vessels, sections are made of tissues that have been fixed in Miiller's fluid, chromic acid, etc. If the specimens are to be studied in detail, small pieces must be used, and are best fixed in chromic-osmic mixtures or corrosive sublimate. Celloidin imbedding is recommended for general topographic work. The further treatment is elective.
The endothelium of the intima may be brought to view by silver nitrate impregnation methods, by injecting silver solutions into the vascular system. The endothelial elements of the smallest vessels and capillaries are then clearly defined by lines of silver. Larger vessels must be cut open, the intima separated, and pieces of its lamellae examined.
Elastic elements, plates and networks are best observed in the tunica media of the vessels, very small pieces of which are treated for some hours with 33% potassium hydrate.
The appropriate stains for sectionwork are those which bring out the elastic elements and the smooth muscle-cells. For the former, orcein is used.
For demonstrating the distribution of the capillaries, the reader is referred to the injection methods. The lymph-capillaries are injected by puncture ; compare also the methods of Altmann.
IV. ORGANS OF RESPIRATION
A. THE LARYNX.
THE greater portion of the laryngeal mucous membrane is covered by a stratified columnar ciliated epithelium containing goblet cells, and resting on a thick basement membrane. The epithelium covering the free margin of the epiglottis, the true vocal cords, and
Glands in false vocal cord.
Stratified pavement ._ epithelium of true \ vocal cord. \
I
Stratified ciliated columnar epithelium.
Glands. __
-Muscle.
Muscle.
Fig- 245. Vertical section through the mucous membrane of the human larynx ; X 5
3IO ORGANS OF RESPIRATION.
part of the arytenoid cartilage as far as the cavity between these cartilages, is of the stratified squamous variety, and is provided with connective-tissue ridges and papillae. The mucosa consists of fibrous connective tissue, contains many elastic fibers, which become larger and more prominent as the deeper layers of the mucosa are approached, and is rather firmly connected with the structures underneath it, but is somewhat more loosely connected in the regions supplied with squamous epithelium. The mucosa contains numerous lymphocytes and leucocytes, which now and then, especially in the region of the Ventricles, form simple follicles. In it are found branched tubulo-alveolar glands, which may be single or arranged in groups. These are found at the free posterior portion of the epiglottis, in the region of the latter' s point of attachment i. e., in the so-called cushion of the epiglottis. Larger collections of glands are found in the false vocal cords, and on the cartilages of Wrisberg (cuneiform cartilages), which appear almost imbedded in the glandular tissue and in the ventricles. In the remaining parts of the larynx glands are found only at isolated points. The true vocal cords have no glands. The glands of the larynx are of the mucous variety, containing crescents of Gianuzzi.
The cartilages of the larynx are of the hyaline variety, with the exception of the epiglottis, the cartilages of Santorini (the latter are derivatives of the epiglottis, Goppert), the cuneiform cartilages, the processus vocalis, and a small portion of the thyroid at the points of attachment of the vocal cords, which consist of elastic cartilage.
The vascular supply of the larynx is arranged in three superimposed networks of blood-vessels. The capillaries are very fine, and lie directly beneath the epithelium. The lymphatic network is arranged in two layers, the superficial being very fine and directly beneath the network of blood capillaries.
The nerves of the laryngeal mucous membrane will be described in connection with those found in the trachea.
B. THE TRACHEA.
The trachea is lined by a stratified ciliated columnar epithelium containing goblet cells and resting on a well-developed basement membrane. The mucosa is rich in elastic tissue. In the superficial portion of the mucosa the elastic fibers form dense strands, which usually take a longitudinal direction. The deeper layer of the mucosa is more loosely constructed, and passes over into the perichondrium of the semilunar cartilages of the trachea without any sharp line of demarcation. Numerous leucocytes are scattered throughout the mucosa, and are also frequently found in the epithelium. Connecting the free ends of the semilunar cartilages, which are of the hyaline variety, are found bundles of nonstriated muscle tissue, the direction of which is nearly transverse.
THE BRONCHI, THEIR BRANCHES, AND THE BRONCHIOLES. 3! I
The trachea contains numerous branched tubulo-alveolar glands of the mucous variety containing here and there crescents of Gianuzzi. The glands are especially numerous where the tracheal wall is devoid of cartilage.
The larynx and trachea receive their nerve supply from sensory nerve-fibers and sympathetic neurones. These have been described by Ploschko (97) working in Arnstein's laboratory. According to this observer, the sensory fibers divide in the mucosa, forming subepithelial plexuses from which fibrils are given off which enter the epithelium of the larynx and trachea and, after further division, end on the epithelial cells in small nodules, or small clusters of nodules. In the trachea of the dog, such fibrils were traced to the ciliary border of the columnar ciliated cells before terminating. Numerous sympathetic ganglia are found in the larynx and trachea. In the latter they are especially numerous in the posterior wall. The neuraxes of the sympathetic neurones forming these ganglia were traced to the nonstriated muscular tissue of the trachea. The cellbodies of these sympathetic neurones are surrounded by end-baskets of small medullated fibers terminating in the ganglia. Medullated
Fig. 246. From longitudinal section of human trachea, stained in orcein: a, Layer of
elastic fibers ; i>, cartilage.
nerve-fibers, ending in the musculature of the trachea in peculiar end-brushes, were also described by Ploschko.
C THE BRONCHI, THEIR BRANCHES, AND THE BRONCHIOLES.
The primary bronchi and their, branches show the same general structure as the trachea, showing, however, irregular plates and platelets of cartilage instead of half-rings, which surround the bronchi. The cartilage is absent in bronchial twigs of less than
3 I2
ORGANS OF RESPIRATION.
0.85 mm. in diameter. The epithelium of the bronchi of medium size (up to 0.5 mm. in diameter) consists of a ciliated epithelium having three strata of nuclei. Kolliker (81) distinguishes a deep layer of basilar cells, a middle layer of replacing cells, and a superficial zone consisting of ciliated and goblet cells. The number of the last varies greatly. Glands are found only in bronchial twigs that are not less than I mm. in diameter ; as in the trachea, they are branched tubulo-alveolar glands of the mucous variety. In these structures the mucosa contains a large number of elastic fibers, the greater part of which have a longitudinal direction. Furthermore, numerous lymph-cells are found, and here and there a lymph-nodule. The muscularis presents, as a rule, circular fibers, which do not, however, form a continuous layer.
The smaller bronchi subdivide into still finer tubules of less than 0.5 mm. in diameter (bronchioles), which contain neither car
stratified cili
.__ ated columnat
epithelium.
Elastic fibers, cut transversely.
- Gland.
5vr Mucosa.
--8 a Cartilage.
Connective tissue.
Fig. 247. Transverse section through human bronchus ; X 2 7 tilage nor glands. The stratum proprium, as well as the external connective-tissue sheath, becomes very thin ; and the epithelium now consists of but one layer,, but is still ciliated.
TERMINAL DIVISIONS OF BRONCHI AND ULTIMATE AIR-SPACES. 313
D. TERMINAL DIVISIONS OF BRONCHI AND ULTIMATE
AIR-SPACES.
The bronchioles are continued as the respiratory bronchioles.
Lung tissue.
Bronchiole.
Fig. 248.
Respiratory _ bronchiole.
Alveolar duct.
-Lung tissue.
Fig. 249.
Figs. 248 and 249. Two sections of cat's lung : Fig. 248, X 5 2 > Fig. 249, X 35 The epithelium of the latter is ciliated in patches, but soon becomes nonciliated and assumes the character of respiratory epithelium.
ORGANS OF RESPIRATION.
(See below.) The walls of the respiratory bronchioles are relatively thin, consisting of fibro-elastic connective tissue and nonstriated muscle. Our knowledge of the further divisions of the bronchioles and of their relation to the terminal air-spaces has been increased greatly by Miller, who has made use of Born's method of wax-plate reconstruction in the study of these structures. His account is here followed. According to Miller, the respiratory bronchioles divide into or become the terminal bronchioles or alveo
Section of al
veolus of lung.
_ Respiratory
bronchiole with two kinds of epithelium.
Respiratory bronchiole.
Fig. 250. Internal surface of a human respiratory bronchiole, treated with silver nitrate ; X 2 34 (after Kolliker).
lar ducts. These are somewhat dilated at their distal ends and communicate, by means of three to six round openings, with a corresponding number of spherical cavities, known as atria. Each atrjum communicates with a variable number of somewhat irregular spaces or cavities, the air-sacs, the walls of which are beset with numerous somewhat irregular hemispheric bulgings, the air-cells or lung alveoli. The air-cells or alveoli are also numerous in the walls of the atria and the terminal bronchioles or alveolar ducts,
TERMINAL DIVISIONS OF BRONCHI AND ULTIMATE AIR-SPACES. 315
and may even be found in the walls of the respiratory bronchioles. The terminal bronchioles or alveolar ducts have an epithelium which is of the cubic variety in their proximal portions, and which changes to a squamous epithelium in their distal portions.
The epithelium of the distal portions of the terminal bronchioles or alveolar ducts, atria, and air-sacs (i I fj. to 15 fj. in diameter) and of the alveoli (the so-called respiratory epithelium) consists of two varieties of cells (F. E. Schulze) smaller nucleated elements and larger nonnucleated platelets (the latter derived very probably from the former). The arrangement of the epithelial cells is generally such that the nonnucleated platelets rest directly upon the blood capillaries, while nucleated cells lie between them. In amphibia the epithelium of the alveoli consists of cells, of which the portion containing the nucleus forms a broad cylindric base; from
^jjjgrjj Nonnucleated epithelial cell.
Nucleated epithelial
cell.
Fig. 251. Inner surface of human alveolus treated with silver nitrate, showing respiratory epithelium ; X 2 4 (after Kolliker).
the free end of each cell a lateral process extends over the adjoining capillary to meet a similar process from the neighboring cell. When viewed from above, the basal portion of the cell appears dark and granular, while the processes are clear and transparent. These cells, together with their prolongations, are about 50 [J. in diameter. The surface view greatly resembles that of the human respiratory epithelium (Duval, Oppel, 89).
The terminal bronchioles or alveolar ducts have a distinct layer of nonstriated muscle having annular thickenings about the openings which lead to the atria. Muscular tissue is not found in the walls of the atria, air-sacs, and air-cells or alveoli (Miller).
Beneath the respiratory epithelium in the atria, air-sacs, and aircells, there is found a thin basement membrane, which is apparently homogeneous. Here and there are found some fibrils of fibrous
ORGANS OF RESPIRATION.
tissue and fixed connective-tissue cells. Elastic fibers are, however, numerous, forming networks beneath the basement membrane.
The work of Miller has given a clearer conception of what may be regarded as the units of lung structure, namely, the lobules. Such a unit or lobule is composed of a terminal bronchiole or alveolar duct, with the air-spaces atria, air-sacs, and air-cells connected with it, and their blood- and lymph-vessels and nerves. The general arrangement of these structures may be observed in Fig. 253, which gives a diagram of a lung lobule. The shape of the atria, air-sacs, and air-cells may be seen in Fig. 254, which is from a wax reconstruction of these structures.
The blood-vessels of the lung, including their relation to the structures of the lung lobules, have been investigated by Miller ; his account is closely followed in the following description: The pulmonary artery follows closely the bronchi through their entire length. An arterial branch enters each lobule of the lung at its apex in close proximity to the terminal bronchiole. After entering the lobule the artery divides quite abruptly, a branch going to each atrium ; from these branches the small arterioles arise which supply the alveoli of the lung. " On reaching the air-sac the artery breaks up into small radicals which pass to the central side of the sac in the sulci between the air-cells, and are finally lost in the rich system of capillaries to which they give rise. This network surrounds the whole airsac and communicates freely with that of the surrounding sacs." This capillary network is exceedingly fine and is sunken into the epithelium of the air-sacs so that between the epithelium and the capillary there is only the extremely delicate basement membrane. Only one capillary
network is found between any two contiguous air-cells or airsacs. The atria, the alveolar ducts and their alveoli, and the alveoli of the respirator}- bronchioles are supplied with similar capillary networks. The veins collecting the blood from the lobules lie at the periphery of the lobules in the interlobular connective tissue, and are as far distant from the intralobular arteries as possible. These veins unite to form the larger pulmonary veins. The bronchi, both large and small, as well as the bronchioles, derive their blood supply from the bronchial arteries, which also partly supply the lung itself. Capillaries derived from these arteries surround the bronchial system, their caliber varying according
Fig. 252. Scheme of the respiratory epithelium in amphibia : The upper figure gives a surface view : f>, Basilar portion ; a, the thin process. The lower figure is a section : <?, Respiratory epithelial cell ; b, bloodvessel ; c, connective tissue around the alveoli.
TERMINAL DIVISIONS OF BRONCHI AND ULTIMATE AIR-SPACES. 3 I /
to the structure they supply finer and more closely arranged in the mucous membrane, and coarser in the connective-tissue walls. In the neighborhood of the terminal bronchial tubes the capillary nets anastomose freely with those of the respiratory capillary system. From the capillaries of the bronchial arteries, veins are formed which empty either into the bronchial veins or into the branches of the pulmonary veins.
<$
Fig. 253. Scheme of lung lobule after Miller : b. r. , Respiratory bronchiole ; d. al., alveolar duct (terminal bronchus); a, a, a, atria; s. al., air-sacs; a. /., aircells or alveoli.
A
Fig. 254. Reconstruction in wax of a single atrium and air-sac with the alveoli : V, Surface where atrium was cut from alveolar duct ; P, cut surface, where another air-sac was removed ; A, atrium ; S, air-sac with air-cells (alveoli) (after Miller).
The lymphatics of the lung are classified by Miller as follows : (#) lymphatics of the bronchi ; (<) lymphatics of the arteries ; (c) lymphatics of the veins; (d} lymphatics of the pleura. The bronchial lymphatics are arranged in two plexuses as far as cartilage is present in the walls of the bronchi, one internal and one external to the cartilage. Beyond the cartilage only a single plexus is found. In the terminal bronchioles there are found three lymphatic vessels, two of which pass to the vein and one to the artery of the lobules. No lymphatics are found beyond the terminal bronchioles. The larger arteries are accompanied by two lymphatic vessels; the smallfer ones, only one. The same is true in general of the lymphatics accompanying the vein. The bronchial lymphatics and those accompanying the arteries and veins anastomose in the regions of the divisions of the bronchi. The pleura possesses a rich network of lymphatics with numerous valves.
Accompanying the bronchi and bronchial arteries are found numerous nerve -fibers, of the nonmedullated and medullated varieties, arranged in bundles of varying size, in the course of which are found sympathetic ganglia. Berkley (94), who has studied the distribution of the nerves of the lung with the chrome-silver method, finds that in the external fibrous layer of the bronchi is found a
ORGANS OF RESPIRATION.
plexus of very fine and of coarser fibers, from which branches are given off which end in the muscle tissue of the bronchi, and others which pass through this layer to form, after further division, a sub
Fig. 255. From section of human lung stained in orcein, showing the elastic fibers surrounding the alveoli.
Blood capillaries
seen in surface
view.
Alveolus in crosssection.
Fig. 256. Section through injected lung of rabbit.
epithelial plexus from which fibrils may be traced into the connective-tissue folds in the larger bronchi and between the bases of the epithelial cells in the smaller bronchi and bronchioles. Some few fibrils were traced between alveoli situated near bronchi, " terminating, apparently, immediately beneath the pavement epithelium in an elongated or rounded minute bulb ; " these may, however, repre
THE THYROID GLAND. 319
sent endings on nonstriated muscle tissue. The bronchial arteries have an exceedingly rich nerve supply.
The visceral and parietal layers of the pleura consist of a layer of fibrous tissue containing numerous elastic fibers. Both layers are covered by a layer of mesothelial cells. The presence of stomata in the pleural mesothelium is denied by Miller. The blood-vessels of the visceral layer of the pleura arise, according to Miller, from the pulmonary artery, these forming a wide-meshed network, which empty into veins which pass into the substance of the lung. Sensory nerve-endings, similar to those found in connective tissue, have been observed in the parietal layer of the pleura.
E. THE THYROID GLAND,
The thyroid gland is developed from three sources : Its middle portion, the isthmus of the gland, and a portion of the lateral lobes originate as a diverticulum of the pharyngeal epithelium, from what
S|
- v
__- SBB^rf^V&.'St' fc/'^'V $*. '
&J:i' f "f^l
^8E
h?5' ^ftsfifg
'
Fig. 257. Portion of a cross-section of thyroid gland of a man ; X 3- &dgj Interstitial
connective tissue ; bg, blood-vessel ; c, colloid substance ; fs, gland alveoli.
is later the foramen caecum of the tongue; a part of both lateral portions, the right and left lobes, are formed from a complicated metamorphosis of the epithelium of the fourth visceral pouch. These various parts unite in man into one, so that in the adult the structure of the organ is.continuous. The thyroid gland consists of numerous noncommunicating acini or follicles of various sizes lined
32O ORGANS OF RESPIRATION.
by a nearly cubic epithelium ; the lobules are separated from each other by a highly vascularized connective tissue, continuous with the firm connective-tissue sheath surrounding the whole gland. The connective -tissue framework of the thyroid has been studied by Flint by means of the destructive digestion method. Relatively greater amounts of connective tissue are found in connection with the bloodvessels, while the follicular membranes are delicate. The follicles are either round, polyhedral, or tubular, and are occasionally branched (Streiff). At an early stage the acini are found to contain a substance known as "colloid" material.
Langendorff has shown that two varieties of cells exist in the acini of the thyroid body the chief cells and colloid cells. Those of the first variety apparently change into colloid cells, while the latter secrete the colloid substance. During the formation of this material the colloid cells become lower, and their entire contents, including the nuclei, change into the colloid mass. Hiirthle distinguished two processes of colloid secretion ; in the one the cells remain intact, in the other they are destroyed. He claims that the colloid cells of Langendorff participate in the former process, while in the latter they are first modified (flattened) and then changed into the colloid substance. The secretion is formed in the cells in the form of secretory granules. The colloid material may enter the lymph-channels, either directly by a rupture of the acini, or indirectly by a percolation of the substance into the intercellular clefts, whence it is carried into the larger lymphatics.
The thyroid gland has a very rich blood supply. The vessels, which enter through the capsule, break up into smaller branches which form a very rich capillary network surrounding the follicles. The veins, which are thin-walled, arise from this capillary network. The gland is provided with a rich network of lymphatic vessels.
Anderson (91) and Berkley (94) have studied the distribution of the nerve-fibers of the thyroid gland with the chrome-silver method ; 'the account given by the latter is the more complete and will be followed here. The nonmedullated nerves entering the gland form plexuses about the larger arteries, which are less dense around the smaller arterial branches. Some of these nerve-fibers are vascular nerves and end on the vessels ; others form perifollicular meshes surrounding the follicles of the gland. From the network of nervefibers about the follicles, Berkley was able to trace fine nerve filaments which seemed to terminate in end-knobs on or between the epithelial cells lining the follicles. Even in the best stained preparations, however, not nearly all the follicular cells possess such a nerve termination. In methylene-blue preparations of the thyroid gland (Dr. De Witt) some few medullated fibers were found in the nerve plexus surrounding the vessels. In a number of preparations these were traced to telodendria situated in the adventitia of the vessels, showing that at least a portion of these medullated nerves are sensory nerves ending in the walls of the vessels.
THE THYROID GLAND.
3 2I
PARATHYROID GLANDS.
Small glandular structures found on the posterior surfaces of the lateral lobes of the thyroid were discovered by Sandstrom in 1880. They are surrounded by a thin connective-tissue capsule and divided into small imperfectly developed lobules by a few thin fibrous-tissue septa or trabeculae, which support the larger vessels. The epithelial portions of these structures consist of relatively large cells and capillary spaces. According to Schaper (95), who has recently subjected these structures to a careful investigation, the epithelial cells have a diameter which varies from 10 /i to 12 //, possessing nuclei 4 // in diameter. These cells are of polygonal shape and have a thin cell-membrane, a slightly granular protoplasm, and a nucleus presenting a delicate chromatic network. The cells are arranged either in larger or smaller clusters or, in some instances, in anastomosing trabeculae or columns, consisting either of a single row or of several rows of cells. Between the clusters or columns of cells are found rela
W&glp*
Fig. 258. From parathyroid of man.
tively large capillaries, the endothelial lining of which rests directly on the epithelial cells. Connective-tissue fibrils do not, as a rule, follow the capillaries between the cell-masses. These vessels may therefore be regarded as sinusoids (Minot). The structure of the parathyroid resembles in many respects that of certain embryonic stages of the thyroid, and it has been suggested that these bodies represent small masses of thyroid gland tissue, retaining their embryonic structure. Schaper has observed parathyroid tissue, the cells of which were here and there arranged in the form of small follicles, some of which contained colloid substance. Such observations lend credence to the view regarding the parathyroid as an embryonic structure. Whether in this stage they form a special secretion has not been fully determined. (See Schaper, 95.)
322 ORGANS OF RESPIRATION.
TECHNIC.
For the demonstration of the larynx and trachea, young and healthy subjects should be selected. Pieces of the mucous membrane or the whole organ should be immersed in a fresh condition. Sections through the entire organ present only a general structural view ; but if a close examination of accurately fixed mucous membrane be desired, the latter should be removed with a razor before sectioning and treated separately.
Chromic-osmic acid mixtures are recommended as fixing agents, and safranin as a stain. Besides the nuclear differentiation, the goblet cells stain brown, and the elastic network of the stratum proprium and the submucosa a reddish -brown.
For examining the epithelium, isolation methods are employed, such as the y$ alcohol of Ranvier.
The examination of the respiratory epithelium is attended with peculiar difficulty ; it is, perhaps, best accomplished by injecting a 0.5% solution of silver nitrate into the bronchus until the lumen is completely filled, and then placing the whole in a 0.5% solution of the same salt. After a few hours, wash with distilled water and transfer to 70% alcohol. Thick sections are now cut and portions of the respiratory passages examined ; the silver lines represent the margins of the epithelial cells. Such sections should not be fastened to the slide with albumen, as the latter soon darkens and blurs the picture. These specimens may also be stained.
For the elastic fibers, especially those of the alveoli, fixation In Miiller's fluid or in alcohol and staining with orcein is a good method, as also Weigert's differential elastic tissue stain. Fresh pieces of lung tissue treated with potassium hydrate show numerous isolated elastic fibers.
Pulmonary tissue may be treated by Golgi's method, which brings out a reticular connective-tissue structure in the vessels and alveoli.
The pulmonary vessels may be injected with comparative ease.
The thyroid gland is best fixed in Flemming's solution ; it is then stained with M. Heidenhain's hematoxylin solution or, better still, with the Ehrlich-Biondi mixture which differentiates the chief from the colloid cells ; the former do not stain at all, while the latter appear red with a green nucleus (Langendorff). The colloid substance of the thyroid gland does not cloud in alcohol or chromic acid, nor does it coagulate in acetic acid, but swells in the latter; 33% potassium hydrate hardly causes the colloid material to swell at all, though in weaker solutions it dissolves after a long time.
THE URINARY ORGANS. 323
V. THE GENITOURINARY ORGANS.
A. THE URINARY ORGANS. J. THE KIDNEY.
THE kidney is a branched tubular lobular gland, which in man consists of from ten to fifteen nearly equal divisions of pyramidal shape known as the renal lobes. The apex of each pyramid (the Malpighian pyramid) projects into the pelvis of the kidney. The kidney is surrounded by a thin but firm capsule consisting of fibrous connective tissue a --^^^^^^^^^^ta^- Artery containing a few elastic fibers and, in its Vein. _j_
deeper portion, a thin ^8l*i|JiyP|g| l^jiP^^
layer of nonstriated
muscle-cells Fig< 2 ^ 9 ' Kidne y of new-born infant, showing a
. distinct separation into reniculi ; natural size. At is
The Secreting por- seen the consolidation of two adjacent reniculi.
tion is composed of a
large number of tubules twisted and bent in a definite and typical manner, the uriniferous tubules. In each one of these tubules we distinguish the following segments : (i) Bowman's capsule, or the ampulla, surrounding a spheric plexus of capillaries, the glomerulus, which, with the capsule of Bowman, forms a Malpighian corpuscle ; (2) a proximal convoluted portion ; (3) a U-shaped portion, consisting of straight descending and ascending limbs and the loop of Henle ; (4) a distal convoluted portion or intercalated portion ; and (5) an arched collecting portion ; from the confluence of a number of these are formed the larger straight collecting tubules, which, in turn, finally unite to form the papillary ducts or tubules of Bellini, which pass through the renal papillae and empty into the renal pelvis. Besides the uriniferous tubules the kidney contains a complicated vascular system, a small amount of connective tissue, etc.
In a longitudinal median section the kidney is seen to be composed of two substances, the one, the medullary substance, possessing relatively few blood capillaries and containing straight collecting tubules and the loops of Henle ; the other, the cortical substance, richer in blood-vessels, and containing principally the Malpighian corpuscles and the proximal and distal convoluted tubules. In each renal lobe we find these two substances distributed as follows : The Malpighian pyramid consists entirely of medullary substance, which sends out a large number of processes, the medul
3 2 4
THE GENITOURINARY ORGANS.
lary rays, or pyramids of Ferrein, toward the surface of the kidney. The latter do not, however, quite reach the surface, but terminate at a certain distance below it ; they are formed by collecting tubules which extend beyond the medullary substance. The entire remaining portion of the kidney is composed of cortical substance ; between the medullary rays it forms the cortical processes, and at the periphery of the kidney, where the medullary rays are absent, the cortical labyrinth. Those portions of the cortical substance separating the Malpighian pyramids are known as the columns of Bertini, or septa renis.
B C
d
Fig. 260. Isolated uriniferous tubules : A and B, from mouse ; C, from turtle. In all three figures a represents the Malpighian corpuscle ; b, the proximal convoluted tubule; c, the descending limb of Henle's loop; d, Henle's loop; e, the straight collecting tubule ; f, the arched collecting tubule.
The various segments of the uriniferous tubule are characterized by their shape and size and by their epithelial lining.
The Malpighian corpuscle has a diameter of from I2O// to 220 p. The capsule surrounding the glomerulus consists of two layers, which are to be distinguished from each other when its relation to the glomerulus is taken into consideration. The capsule forms a double-walled membrane around the glomerulus ; a condition which is easily understood by imagining an invagination of the
THE URINARY ORGANS.
325
glomerulus into the hollow capsule. Between the inner wall covering the surface of the glomerulus (glomerular epithelium) and the outer wall (Bowman's capsule) there remains a cleft-like space which communicates with the lumen of the corresponding uriniferous tubule. In the adult the glomerular epithelium is very flat, with nuclei projecting slightly into the open space of the Malpighian corpuscle. The epithelium of the outer wall is somewhat higher, but still of the squamous type. The capsule of Bowman communicates with the proximal convoluted tubule by means of a short and narrow neck. Its epithelium passes over gradually into
Column of Bertini.
Malpighian pyramid.
Lobule of adipose tissue.
Blood-vessel.
f Papilla.
~f Ureter.
Fig. 261, Median longitudinal section of adult human kidney ; nine-tenths natural size. In the peripheral portion the limits between its renal lobes are no longer recognizable.
the cubical epithelium of the neck, which, in turn, merges into that of the proximal convoluted tubule.
The proximal convoluted portion is from 40 [i to 70 // in diameter and is lined by a single layer of irregular columnar cells, the boundaries of which are made out with difficulty. The structure of these cells has been studied in recent years by a number of investigators, among whom may be mentioned Disse, whose account
326
THE GENITOURINARY ORGANS.
is here followed. In the epithelial cells of the proximal convoluted portion there may be recognized an outer or basal portion of the cells, in which there is found a spongioplastic network with rectangular meshes, with cytoreticular fibrils running parallel and at right angles to the basement membrane. In the meshes of this network there is found hyaloplasm. The cytoreticular fibrils which are at right angles to the basement membrane contain numerous granules, giving the basal portions of the cells a striated appearance. The inner portions of the cells contain a cytoreticulum and hyaloplasm; the reticular fibrils do not, however, contain granules,
a b
Fig. 262. From section of cortical substance of human kidney ; X 2 4 : a Epithelium of Bowman's capsule; b and d, membrana propria ; c, glomerular epithelium;
g, blood-vessels ; f, lobe of trie glomerulus ; g, commencement of uriniferous tubule ;
A, epithelium of the neck ; i, epithelium of proximal convoluted tubule.
the inner portions of the cells presenting, therefore, a much less striated appearance than the outer portions. In tissues not well fixed there is often observed in the cells a free border which presents the appearance of being made of stiff fibrils or coarse and short cilia, which has been interpreted as a distinctive structure. Such a striated border is in all probability a result of partial disintegration or maceration of the cells. The nucleus of these cells is of nearly spheric shape and is situated in the inner part of the basal portions of the cells. The cells, especially in their inner non-striated regions, are so intimately connected that the cell limits are not always distinguishable. In the guinea-pig the basal regions of the lateral
THE URINARY ORGANS.
surfaces of the cells constituting the epithelium of the proximal convoluted portion present numerous projections which interlock and give to a surface view an irregular fringe-like outline. In crosssection the cells appear to be striated from their bases upward to the middle of the nucleus. Here, however, the striation is without doubt due to the outlines of the irregular ridges. (Fig. 264.) These structural relations have lately been confirmed in the case of the guinea-pig, and also found to hold true for man (Landauer). This striation is much coarser than that found in the basal portions of the cells, but both are, under certain circumstances, seen together.
Nuclei of endothe 1 ial
cells of blood
capillaries.
Lumen of uriniferous tubule.
Striated border.
Fig. 263. Section of proximal convoluted tubules from man ; X S% The proximal convoluted portion of the uriniferous tubule, before it terminates, passes over into a straighter portion, which gradually becomes smaller in diameter, and is situated in the medullary rays. This portion of the uriniferous tubule, which is sometimes designated as the spiral segment of Schachowa, or again as the end segment of Argutinski, is lined by an epithelium which is similar to that of the proximal convoluted portion, as above described. The attenuated end of the spiral segment is continuous with the descending limb of Henle's loop.
The descending limb of Henle's loop, from g/j. to 15^ in diameter, is narrow and possesses flattened epithelial cells, the centers of
328
THE GENITOURINARY ORGANS.
which, containing the nuclei, project into the lumen of the tubule. These central projections of the cells are not directly opposite those of the cells on the opposite wall, but alternate with the latter, thus
Nucleus
ON- -Nucleus.
Fig. 264. Epithelium from proximal convoluted tubule of guinea-pig, with surface and lateral views (chrome-silver method) ; X 59 : a > a > The irregular interlacing projections.
iV^'-iP^* 1 -
-"*&- ^
Fig. 265. From cortical portion of longitudinal section of kidney of young child.
giving to the lumen a zigzag outline corresponding to the length of the cell. The thick portion of the loop, for the most part represented by the ascending limb, but generally embracing the loop itself,
THE URINARY ORGANS.
329
from 23 fi. to 28 fji in diameter, possesses a columnar epithelium similar to that of the proximal convoluted portion. Here, however, the basal striation of the cells is not so distinct, the lumen is somewhat larger than that of the descending limb, and by treatment with certain reagents the epithelium may often be separated as a whole from the underlying basement membrane.
The distal convoluted or intercalated portion (segment of Schweigger-Seidel), from 39 /j. to 45 f* in diameter, is only slightly curved (2 to 4 convolutions). Its epithelium is relatively high, though not so high as that lining the proximal convoluted portion and not so distinctly striated, though containing numerous granules. The cells are provided with large nuclei and their basal portions are joined by interlacing projections.
a.
5asSf;0*jv .-, g*
^itf^vW
_J $&- M - Jv '*>?'"
4/-"'^ c;i ^' i.^^gSr'i
> vC v p:p^
<--- .9g^'.D^>. sa'./!*
4
,-,"J? . .. EW^34&=-,.
-^"' &' : ^X^^W;^ e) ^^ &
&-*? * G>^ ;= - c^
Fig. 266. Section of medulla of .human kidney; X about 300: a, 0, a, Ascending
limb of Henle's loop ; b, l>, b, blood-vessels ; c, c, c, descending limb of Henle's loop.
The next important segment is the short arched collecting portion, which has nearly cubical epithelial cells and a lumen somewhat wider than that of the intercalated tubule. The smaller straight collecting tubules have a low columnar epithelium with cells of somewhat irregular shape, the basal portions of which are provided with short, irregular, intertwining processes, which serve to hold the cells in place. The diameter of the collecting tubules measures from 45 // to .
330
THE GENITOURINARY ORGANS.
In the larger collecting tubules the epithelium is more regular and becomes higher as the tube widens. These tubules gradually unite within the Malpighian pyramid and the regions adjacent to the columns of Bertini to form 1 5 to 20 papillary ducts from 200 fj. to 300 // in diameter. The latter have a high columnar epithelium, and empty into the pelvis of the kidney at the apex of the papilla, forming the foramina papillaria in an area known as the area cribrosa.
Besides the epithelium, the uriniferous tubules possess an apparently structureless membrana propria, that of the collecting tubules being very thin. This membrane may be isolated, as has been shown by F. P. Mall, by macerating frozen sections in a cold saturated solution of bichromate of soda for several days. This membrane is digested in pancreatin.
Papillary duct.
Blood-vessel.
Fig. 267. From longitudinal section through papilla of injected kidney ; X 4 : a > Epithelium of collecting tubule under greater magnification.
Between the Malpighian pyramids are found the columns of Bertini, presenting a structure similar to that of the cortex of the kidney, and extending to the hilum of the kidney.
Between the uriniferous tubules and surrounding the bloodvessels of the kidney there is found normally a small amount of stroma tissue, consisting of white fibrous and reticular fibers, elastic fibers being found in connection with the blood-vessels (F. P. Mall, Riihle). Between the convoluted portions of the tubules this is present only in small quantity, the fibrils being felted to form sheaths for the tubules ; a somewhat greater amount being found in the neighborhood of the Malpighian corpuscles, in the boundary zone between the cortex and medulla and between the larger collecting tubules in the apices of the Malpighian pyramids.
From wrmt has been said concerning the uriniferous tubule it must be evident that its course is a very tortuous one. Beginning
THE URINARY ORGANS.
331
with the Malpighian corpuscles, situated in the cortex between the medullary rays, the tubule winds from the cortex to the medulla and back again into the cortex, where it ends in a collecting tubule, which passes to the medulla to terminate at the apex of a Malpighian pyramid. The different portions of the tubules have the following positions in the kidney : In the cortex between the medullary rays are found the Malpighian corpuscles, the neck, the proximal and distal convoluted portions of the uriniferous tubule, and the arched collecting tubules. The medullary rays are formed by the cortical portions of the straight collecting tubules and a portion of
" Boundary line
between two
Malpighian
pyramids.
<~-*~ Uriniferous tubules.
^-Glomerulus.
Fig. 268. Section through junction of two lobules of kidney, showing their
coalescence ; from new-born infant.
the descending and ascending limbs of Henle's loops. The medulla is made up mainly of straight collecting tubules of various sizes and of the descending and ascending limbs and loops of Henle's loops, the latter being often found in the boundary zone between the cortex and medulla. (See Fig. 266.) The ascending limb of Henle's loop of each uriniferous tubule, after it enters the cortex, comes into close proximity with the Malpighian corpuscle of the respective uriniferous tubule.
332 THE GENITOURINARY ORGANS.
The blood-vessels of the kidney have a characteristic distribution, and are in the closest relationship to the uriniferous tubules.
The renal artery, as has been shown by Brodel, divides at the hilum on an average into four or five branches, about three-fourths of the blood-supply passing in front of the pelvis, while one-fourth runs posteriorly. The portion of the kidney supplied by the anterior branches is in its blood-supply quite distinct from that supplied by the posterior branches ; the one set of branches do not cross over to the other. The two ends of the kidney are supplied by an anterior and a posterior branch, each of which generally divides into three branches, which pass respectively, one anteriorly, one posteriorly, and one around the end of the uppermost and the lowest calyx.
The main branches of the renal artery give off lateral branches to the renal pelvis, supplying its mucous membrane and then breaking up into capillaries which extend as far as the "area cribrosa." The venous capillaries of this region empty into veins which accompany the arteries. Besides these, other arteries originate from the principal branches, or from their immediate offshoots, and pass backward to supply the walls of the renal pelvis, the renal capsule, and the ureter. The main trunks themselves penetrate at the hilum, and divide in the columns of Bertini to form arterial arches (arteriae arciformes) which extend between the cortical and medullary substances. Numerous vessels, the intralobular arteries, originate from the arteriae arciformes and penetrate into the cortical pyramids between the medullary rays. Here they give off numerous twigs, each of which ends in the glomerulus of a Malpighian corpuscle. These short lateral twigs are the vasa affcrcntia. Each glomerulus is formed by the breaking down of its afferent vessel, which, on entering the Malpighian corpuscle, divides into a number of branches, five in a glomerulus of a child three months old reconstructed by W. B. Johnston, each in turn subdividing into a capillary net. From each of these nets the blood passes into a somewhat larger vessel constituting one of the branches of the efferent vessel which carries the blood away from the glomerulus. Since the afferent and efferent vessels lie in close proximity, the capillary nets connecting them are necessarily bent in the form of loops. The groups of capillaries in a glomerulus are separated from each other by a larger amount of connective tissue than separates the capillaries themselves, so that the glomerulus may be divided into lobules. In shape the glomerulus is spheric, and is covered by a thin layer of connective tissue over which lies the inner membrane of the capsule, the glomerular epithelium. On its exit from the glomerulus the vas efferens separates into a new system of capillaries, which gradually becomes venous in character. Thus, the capillaries which form the glomerulus, together with the vas efferens, are arterial, and may be included in the category of the so-called arterial retia mirabilia. Those capillaries formed by the vas efferens after its exit from the Malpighian corpuscle lie both in the medullary
THE URINARY ORGANS.
333
rays and in the cortical pyramids. The meshes of the capillary networks distributed throughout the medullary rays are considerably longer than those of the networks supplying the cortical pyramids and labyrinth, the latter being quadrate in shape. The glomeruli nearest the renal papillae give off longer vasa efferentia which extend into the papillary region of the Malpighian pyramids (arteriolae rectae spuriae) and form there capillaries which ramify throughout the papillae with oblong meshes.
Artery cf capsule.
Arched collecting . tubule. '""*---.
Straight collecting tubule. '"*
Distal convoluted tubule.
Malpighian corpuscle.
Proximal convoluted tubule. "---Loop of Henle. ; .-^,_
Collecting tubule.
Arteria arcuata. ___.
[ Glomerulus.
Vena arcuata.
Large collecting tubule.
Papillary duct.
Fig. 269. Diagrammatic scheme of uriniferous tubules and blood-vessels of kidney. Drawn in part from the descriptions of Golubew.
Arterial retia mirabilia also occur in the course of the vasa afferentia between the intralobular arteries and the glomeruli, but nearer the latter. Each is formed by the breaking down of the small afferent vessels into from two to four smaller branches, which then reunite to pass on as a single vessel. In structure these retia differ greatly from the glomeruli in that here the resulting twigs are not capillaries and have nothing to do with the secretion of urine (Golubew).
From the vasa afferentia arterial twigs are occasionally given
334 THE GENITOURINARY ORGANS.
off, which break down into capillaries within the cortical substance. Other arteries originate from the lower portion of the intralobular arteries or from the arciform arteries themselves and enter the medullary substance, where they form capillaries. These vessels constitute the so-called "arteriolae rectae verae." Their capillary system is in direct communication with the capillaries of the vasa afferentia and "vasa recta spuria." The intralobular arteries are not entirely exhausted in supplying the vasa afferentia which pass to the glomeruli. A few extend to the surface of the kidney and penetrate into the renal capsule, where they terminate in capillaries which communicate with those of the recurrent, suprarenal, and phrenic arteries, etc. Smaller branches from these latter vessels may penetrate the cortex and form glomeruli of their own in the renal parenchyma (arteriae capsulares glomeruliferae). These relations, first described by Golubew, are of importance not only in the establishment of a collateral circulation, but also as a partial functional substitute in case of injury to the renal arteries. The same author also confirms the statements of Hoyer (77) and Geberg, that between the arteries and veins of the kidney, in the cortical substance, in the columns of Bertini, and at the bases of the Malpighian pyramids, etc., direct anastomoses exist by means of precapillary twigs.
From the capillaries the venous blood is gathered into small veins which pass out from the region of the medullary rays and cortical pyramids and unite to form the "intralobular veins." These have an arrangement similar to that of the corresponding arteries. The venous blood of the labyrinthian capillaries also flows into the intralobular veins, and as a result a peculiar arrangement of these vessels is seen at the surface of the kidney where the capillaries pass radially toward the terminal branches of the intralobular veins and form the stellate figures known as the vence stellatce. This system is also connected with those venous capillaries of the capsule which do not empty into the veins accompanying the arteries of the capsule. The capillary system of the Malpighian pyramids unites to form veins, the "venulae rectae," which empty into the venous arches (venae arciformes) which lie parallel with and adjacent to the corresponding arteries. The larger veins are found side by side with the arteries and pass out at the hilum of the organ.
Lymphatics of the kidney may be divided into superficial lymphatic vessels, situated in the capsule, and deep ones, found in the substance of the kidney. The deep lymphatic vessels need to be investigated further. They form a network of closed lymphatic vessels throughout the cortex. These empty, according to Rindowsky, into larger lymphatics, which follow the intralobular vessels ; and, according to Stahr, into larger vessels situated in the medullary rays. The lymphatic vessels of the kidney proper (deep vessels) leave this organ at the hilum.
The kidneys receive their innervation through nonmedullated
THE URINARY ORGANS.
335
and medullated nerve-fibers. The former accompany the arteries and may be traced along these to the Malpighian corpuscles. From the plexuses surrounding the vessels small branches are given off, which end on the muscle-cells of the media. According to Berkley, small nerve-fibrils may be traced to the uriniferous tubules, which pierce the membrana propria and end on the epithelial cells. Smirnow has also traced nerve-fibers to the epithelial cells of the uriniferous tubules and the Malpighian corpuscles. Dogiel has shown that medullary (sensory) nerve-fibers terminate in the adventitia of the arteries of the capsule.
The secretory processes of the kidney can be considered only briefly in this connection. The theories concerning uriniferous secretion may be grouped under two heads : namely, the theory of C. Ludwig, who believed that all the constituents of the urine
A
Fig. 270. A, Direct anastomosis between an artery and vein in a column of Berlin
of child ; B, bipolar rete mirabile inserted in the course of an arterial twig. Dog's
kidney (after Golubew).
leave the blood through the glomeruli, entering the uriniferous tubules as a urine containing a large percentage of water, which is concentrated in its passage through the uriniferous tubule by the absorption of water ; while according to the theory of Bowman, and later Heidenhain, only the water and inorganic salts leave the blood through the glomerulus, and that in the proportion found in the urine, while the urea is secreted by the epithelial cells of the uriniferous tubules, and mainly in those portions of the tubules possessing a striated epithelium. The majority of writers who have considered the question of urinary excretion have directly or indirectly expressed themselves as adherents to one or the other of the above theories. A number of recent observers have departed somewhat from either of the above theories, and of these we may
336 THE GENITOURINARY ORGANS.
mention especially the careful researches of Cushny, who brings forth strong proof to show that with the fluid passing through the glomerular epithelium there are carried certain salts and urea, the salts and urea in the proportion in which they occur in the bloodplasma, and that in passage through the uriniferous tubules a certain percentage of the fluids and certain salts are again absorbed, the salts in proportion to their diffusibility or their permeability of the renal cells.
The permanent kidney is developed as early as the fifth week of embryonic life. The renal anlagen, from which the epithelium of the ureter, renal pelvis, and a portion of the uriniferous tubules is formed, originate from the median portion of the posterior wall of the Wolfrian duct. These buds grow with their blind ends extending anteriorly, and are soon surrounded by cellular areas, the blastema of the kidneys. After the renal bud has become differentiated into a narrow tube (the ureter) and a wider central cavity (the renal pelvis) hollow epithelial buds are developed from the latter. These extend radially toward the surface of the renal anlagen, where they undergo a T-shaped division. These latter are the first traces of the papillary ducts and collecting tubules. The ends of these T-shaped divisions are surrounded by a cellular tissue, derived from the mesoderm, which is known as the renal blastema or the nephrogenic tissue. In this tissue there are differentiated spheric masses of cells, which in their further growth differentiate into S-shaped structures one end of which unites with the ends of the epithelial buds, developed as above described. The S-shaped structures acquire a lumen and form the anlagen of the uriniferous tubules, from the arched collecting tubules to and including Bowman's capsule. The ducts of the kidneys, from the papillary ducts to the collecting tubules of the medullary rays, have their origin from the epithelial buds which develop from the side of the Wolfrian ducts, while the uriniferous tubules proper have their origin in the nephrogenic tissues.
2. THE PELVIS OF THE KIDNEY, URETER, AND BLADDER.
The renal pelvis, ureter, and urinary bladder are lined by stratified transitional epithelium. Its basal cells are nearly cubical ; these support from two to five rows of cells of varying shape. They may be spindle-shaped, irregularly polygonal, conical, or sharply angular, and provided with processes. Their variation in form is probably due to mutual pressure. The superficial cells are large and cylindric, a condition characteristic of the ureter and bladder. Their free ends and lateral surfaces are smooth, but their bases present indentations and projections due to the irregular outlines of the underlying cells. The superficial cells often possess two or more nuclei.
THE URINARY ORGANS.
337
The mucosa often contains diffuse lymphoid tissue, which is more highly developed in the region of the renal pelvis. Here also there are found folds or ridges of mucosa which extend into the epithelium and present the appearance of papillae when seen in cross-section. A few mucous glands are also met with in the pelvis and in the upper portion of the ureter in certain mammals; in man, however, no typical glands are found, although solid
Superficial epithelial cells
Epithelium.
Mucosa.
Inner longitudinal muscular layer.
Middle circular muscular layer.
Outer muscular layer.
Fig. 271. Section of lower part of human ureter ; X I 4 epithelial buds, which extend into the mucosa for a distance, have been described. The ureter possesses two layers of nonstriated muscle-fibers the inner longitudinal, the outer circular. From the middle of the ureter downward a third external muscular layer is found with nearly longitudinal fibers.
The urinary bladder has no glands, and its musculature apparently consists of a feltwork of nonstriated muscle bundles, a condi
338
THE GENITOURINARY ORGANS.
tion particularly well seen in sections of the dilated organ. But even here three indistinct muscle layers may be distinguished, the outer and inner layers being longitudinal and the middle circular. A remarkable peculiarity of these structures is the extreme elasticity of their epithelium, the cells flattening or retaining their natural shape according to the amount of fluid in the cavities which they
- '**'**
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fu'M iU\Ui
V? ff-lVVAl
1 ; I- '*! ' vl
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.':. 'fW : '. '
/
' ' "*' '^"tf' ' i ' >f ^; , s .2ijK
- \'rp>;; .,; vp*^ :
I
\*. ' . . . X.
aim.
77W
Fig. 272. Transverse section of the wall of the human bladder, giving a general view of its structure. X 1 5- e Pi Epithelium; tp, tunica propria or mucosa; sw, submucosa ; ilm, inner longitudinal layer of muscle ; rin, circular layer of muscle ; aim, external longitudinal layer of muscle ; fa, tunica adventitia.
line (compare London, Kann). The terminal blood-vessels of the mucosa of the pelvis of the kidney deserve special mention. The capillaries arise from arterioles which are situated in the ridges of the mucosa above mentioned. The capillaries are peculiar in that they are not completely surrounded by connective tissue, but are in part embedded in the epithelium, the epithelial cells resting on the endothelial wall of the capillaries (Disse). The blood-vessels of the bladder anastomose in the tunica adventitia, smaller branches pass to the muscular tissue. The main stems of the vessels form a plexus in the submucosa, from which arise the capillaries of the mucosa. The veins form submucous, muscular, and subperitoneal plexuses (Fenwick). Lymphatic vessels are found only in the muscular coat and not in the mucosa.
THE SUPRARENAL GLANDS. 339
The nerve supply of the bladder has been studied by Retzius, Huber, and Griinstein in the frog and a number of the smaller mammalia. Numerous sympathetic ganglia are observed, situated outside of the muscular coat, at the base and sides of the bladder. The neuraxes of the sympathetic neurones of these ganglia are grouped into smaller or larger bundles which interlace and form plexuses surrounding the bundles of nonstriated muscle-cells. From these plexuses nerve-fibers are given off, which penetrate the muscle bundles and end on the muscle-cells. The cell-bodies of the sympathetic neurones are surrounded by the telodendria of small medullated fibers, which terminate in the ganglia. Passing through the ganglia large medullated fibers (sensory nerves) may be observed which pass through the muscular coat, branch repeatedly in the mucosa, and lose their medullary sheat'hs on approaching the epithelium in which they end in numerous telodendria, the small branches of which terminate between the epithelial cells.
The ureters are surrounded by a nerve plexus containing nonmedullated and medullated nerve-fibers. The former end on cells of the muscular layers ; the latter pass through the muscular layer, and on reaching the mucosa branch a number of times before losing their medullary sheaths. The nonmedullated terminal branches form telodendria, the terminal fibers of which have been traced between the cells of the lining epithelium (Huber).
B. THE SUPRARENAL GLANDS.
The suprarenal gland is surrounded by a fibrous-tissue capsule containing nonstriated muscle-cells, blood- and lymph-vessels, nerves, and sympathetic ganglia. The glandular structure is divided into a cortical and a medullary portion. In the former are distinguished three layers, according to the arrangement, shape, and structure of its cells an outer glomerular zone, a middle broad fascicular zone, and an inner reticular zone. According to Flint, who worked in F. P. Mall's laboratory, and whose account will here be followed, the framework of the gland is made up of reticulum. In the glomerular zone this reticulum is arranged in the form of septa, derived from the capsule, which divide this zone into more or less regular spaces of oval or oblong shape. In the fascicular zone the reticulum is arranged in processes and fibrils running at right angles to the capsule. In the reticular zone the fibrils form a dense network, while in the medulla the reticular fibrils are arranged in processes and septa which outline numerous spaces.
The gland-cells of the glomerular zone are arranged in coiled columns of cells found in the compartments formed by the septa of reticulum above mentioned. The cells composing these columns are irregularly columnar, with granular protoplasm and deeply staining nuclei. In the fascicular zone the cells are arranged in regular
340
THE GENITOURINARY ORGANS.
columns, consisting usually of two rows of cells, and situated between the reticular processes, which run at right angles to the capsule. The cells of this zone are polyhedral in shape, with granular protoplasm often containing fat droplets and with nuclei containing little chromatin. Similar cells are found in the reticular zone, but here they are found in small groups situated in the meshes of the reticulum. The cells of the medullary substance are less granular and smaller in size than those of the cortex, and are grouped in irregular, round, or oval masses bounded by the septa of reticulum. These cells stain a deep brown with chromic acid and its
. Zona fasciculate.
Capsule.
Zona glomerulosa.
Zona reticularis.
Fig. 273. Section of suprarenal cortex of dog ; X 1 2O '
salts are therefore known as chromaffin cells ; the color cannot be washed out with water a peculiarity which shows itself even during the development of these elements, and which is possessed by few other types of cells. Numerous ganglion cells, isolated and in groups, and many nerve-fibers occur in this portion of the organ.
THE SUPRARENAL GLANDS.
341
The blood-vessels of the suprarenal glands are of special interest, since it has been shown that the secretion of the glands passes directly or indirectly into the vessels. The following statements we take from Flint : The blood-vessels, derived from various sources, form in the dog a poorly developed plexus, situated in the capsule. From this plexus three sets of vessels are derived, which are distributed respectively in the capsule, the cortex, and the medulla of the gland. The vessels of the capsule divide into
Fig. 274. Arrangement of the intrinsic blood-vessels in the cortex and medulla of
the dog's adrenal (Fig. 17, Plate V, of Flint's article in " Contributions to the Science
of Medicine," dedicated to Professor Welch, 1900).
capillaries, which empty into a venous pldxus situated in the deeper portion of the capsule. The cortical arteries divide into capillaries which form networks, the meshes of which correspond to the arrangement of the cells in the different parts of the cortex, encircling the coiled columns of cells in the glomerular zone, while in the fascicular zone the capillaries are parallel with occasional anastomoses. These capillaries form a fine-meshed plexus in the reticular zone and unite in the peripheral portion of the
342 THE GENITOURINARY ORGANS.
medulla to form small anastomosing veins, from which the larger veins are derived. The latter do not anastomose, and are therefore terminal veins. The arteries of the medulla pass through the cortex without giving off any branches until the medulla is reached, where they break up into a capillary network surrounding the cell masses situated here. The blood from this plexus may be collected into veins of the medulla which empty into the terminal vein or some of its larger branches, or .may flow directly into branches of the venous tree. The endothelial walls of the capillaries rest directly on the specific gland cells, with the intervention here and there of a few reticular fibrils. According to Pfaundler, the walls of the blood-vessels of the entire suprarenal body consist solely of the tunica intima.
The nerves of the suprarenal glands have been studied recently by Fusari and Dogiel (94) ; the description given by the latter will here be followed. Numerous nerve-fibers, both nonmedullated and medullated, arranged in the form of a plexus containing sympathetic ganglia, are found in the capsule. From this plexus numerous small bundles and varicose fibers enter the cortex, where they form plexuses surrounding the columns of cells or groups of cells found in the three zones of the cortex and about the vessels and capillaries of the cortex. The nerve-fibers of these plexuses are on the outside of the columns and cell groups and do not give off branches which pass between the cells. The nerve supply of the medullary substance is very rich, and is derived mainly from large nerve bundles which pass from the plexus in the capsule to the medulla, where they divide and form dense plexuses which surround the groups of gland-cells and veins ; from these plexuses fine varicose fibers pass between the gland-cells, forming intercellular plexuses. In the medulla there are found in many animals large numbers of sympathetic cells, some isolated, others grouped to form small ganglia. Pericellular networks surround the cellbodies of certain of these sympathetic cells. (For further information concerning the suprarenal glands consult Gottschau, Weldon, Hans Rabl, C. K. Hoffmann (92), Pfaundler, Flint, and Dogiel.)
TECHNIC.
Kidney. The arrangement of the cortical and medullary portions of the kidney is best seen in sections of the kidney of small mammalia, cut in the proper direction, and, if possible, embracing the whole organ. If, on the other hand, the finer epithelial structures are to be examined, small pieces are first fixed in osmic acid mixtures or in corrosive sublimate.
Impregnation with silver nitrate (method of Golgi or Cox) reveals some points as to the relation of the cells of the uriniferous tubules to each other.
In order to isolate the tubules, thin strips of kidney tissue are treated for from fifteen to twenty hours with pure hydrochloric acid
TECHNIC. 343
having a specific gravity of 1.12 (for this purpose kidney tissue is used taken from an animal killed twenty-four hours previously). It is then washed, teased, and examined in glycerin (Schweiger-Seidel). Fuming nitric acid (40%), applied for a few hours to small pieces of tissue, occasionally isolates the uriniferous tubules very extensively. The further treatment is then the same as after hydrochloric acid. A 35% potassium hydrate solution may also be employed. The isolated pieces are, however, not easily preserved permanently.
The epithelium of the uriniferous tubules may be isolated either in YI alcohol or, according to R. Heidenhain (83), in a 5^ aqueous solution of neutral ammonium chromate. The latter method shows clearly the striation of the epithelium.
The autophysiologic injection with indigo-carmin, applied as in the case of the liver, fills the uriniferous tubules, which may then be further examined in sections.
The blood-vessels are examined in injected specimens (injection of the kidney is easily accomplished). In larger animals the injection is made into the renal artery, while in smaller ones the whole posterior half of the body is injected through the abdominal aorta.
The ureter and bladder are cut open, fixed, and then sectioned. In this way the organs are shown in a collapsed condition, in which the arrangement of the epithelium is totally different from that found in the distended organs. In order to observe them in the latter condition the fixing agent is injected into the ureter or bladder, when, after proper ligation, they are placed in the same fixing agent.
The usual fixing fluids are employed in the demonstration of the suprarenal capsule; but mixtures containing chromic acid, whether Flemming's fluid, chromic acid, or its salts, are of special importance in the examination of the organ, since the medullary substance of the suprarenal capsule stains a specific brown when treated by these mixtures (a condition only reduplicated in certain cells of the hypophysis). This brown staining also occurs when the cortical and medullary portions are entirely separated, as is the case in certain animals and during the development of the suprarenal capsule. The fat found in the cells of the suprarenal cortex is not identical with that of the rest of the body, as it may be dissolved by chloroform and oil of bergamot out of tissue fixed with osmic acid (Hans Rabl).
344 THE GENITOURINARY ORGANS.
C THE FEMALE GENITAL ORGANS.
1. THE OVUM.
The product of the ovaries is the matured " ovum," or egg, having a diameter of from 0.22 to 0.32 mm. It forms a single cell with a thick membrane, from 7 /j. to 1 1 // in thickness, known as the zona pellucida. The ovum consists of a cell-body known as the yolk or vitellus, and a nucleus, from 30^ to 40 /J. in diameter, termed the germinal vesicle. The vitellus consists of two substances a protoplasmic network, with a somewhat denser arrangement at the periphery of the cell and in the neighborhood of the germinal vesicle, and of small, highly refractive, and mostly oval bodies imbedded between the meshes of the protoplasm the yolk globules. These latter, as a rule, are merely browned on being treated with osmic acid, although occasionally a true fatty reaction may be obtained. The germinal vesicle is surrounded by a distinct membrane having a double contour. In its interior we find a scanty lining framework containing very little chromatin, and one or two relatively large false nucleoli, or germinal spots, from 7// to lOfJt in diameter, due to a nodal thickening of the chromatin. In the latter a further very distinct differentiation is sometimes seen in the shape of a small body (vacuole?) of doubtful origin, which has been called Schron's granule. The germinal vesicle and spot were formerly known as " Purkinje's vesicle" and "Wagner's spot," respectively, from their discoverers.
2. THE OVARY.
The ovaries are almost entirely covered by peritoneum. The mesothelial cells of the latter, however, undergo here a differentiation, to form the germinal epithelium. At the hilum the peritoneal covering is absent, and it is here that the connective -tissue elements of the ovarian ligament penetrate into the organ to form its connective-tissue framework, the so-called stroma of the ovary. At an early period in the development of the ovaries, the germinal epithelium begins a process of imagination into the stroma of the ovary, so that at the periphery of the organ a zone is soon formed which consists of both connective tissue and epithelial (mesothelial) elements. This zone is called the cortex, or parenchymatous zone. That portion of the organ in the neighborhood of the hilum (aside from the rudimentary structure known as the epoophoron) consists of connective tissue containing numerous elastic fibers and unstriped muscle-cells, and is known as the medullary substance, or vascular zone. This connective tissue penetrates here and there into the cortex, separates the epithelial elements of the latter from each other, and is in direct continuation with a stratum immediately beneath the germinal epithelium, called the tunica albuginea. This latter layer of connective tissue is generally distinct in the adult ovary, although
THE FEMALE GENITAL ORGANS.
345
its structure and thickness vary to a considerable extent. In young ovaries it is irregular, but shows in its highest development three layers distinguishable from each other by the different direction of the fibers. In the medullary substance the connective-tissue fibers are long, in the cortex short, and in the zone containing the follicles (see below) are mingled with numerous connective-tissue cells. Nonstriated muscle-fibers occur exclusively in the medulla. Here they are gathered in bundles which accompany the blood-vessels, and may even form sheaths around the latter. They are especially prominent in mammalia.
The germinal epithelium is distinguished from that of the remaining peritoneum by the greater height of its cells, which are
Young follicle with ovum.
Primordial ova
Ovum with follicular epithelium.
Fig. 275. Section from ovary of adult dog. At the right the stellate figure represents a collapsed follicle with its contents. Below and at the right are seen the tubules of the parovarium (copied from Waldeyer).
cubic or even cylindric in shape. At an early period in the development of the ovaries this epithelium pushes into the underlying embryonic connective tissue in solid projections, to form the primary egg tubes of Pfluger, the cells of which very soon begin to show differentiation. Some retain their original characteristics and shape, while others increase in size, become rounded, and develop into the young ova. Those retaining their indifferent type become the follicular cells surrounding the egg. This differentiation into ova and follicular elements may even occur in the germinal epithelium itself, in which case the larger round cells are known as the primitive or primordial ova. In the further development of the ovarian cortex
346
THE GENITO-URINARY ORGANS.
the primitive egg tubes are penetrated throughout by connective tissue, so that each egg tube is separated into a number of irregular divisions. In this way a number of distinct epithelial nests are formed, which lose their continuity with the germinal epithelium and finally lie imbedded in the connective tissue. According to the shape and other characteristics of these epithelial nests, we may distinguish several different groups: (i) The primitive egg tubes
Germinal epi thelium.
Tunica albu ginea.
Follicular _^ epithelium.
Ovum.
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- 9 v-Qfj ~ "o " ">T*5 **ij3X0 ef'S yGrttJ^OOO
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Granular layer of large Graafian follicle.
Fig. 276. From ovary of young girl ; X I 9
of Pfluger ; (2) the typical primitive follicles i. e., those which
contain only a single egg-cell (present in the twenty-eighth week of
fetal life) ; (3) the atypic follicles i. e., those containing from two
to three egg-cells ; (4) the so-called nests of follicles, in which a
large number of follicles possess only a single connective-tissue envelope ; (5) follicles of the last-named type which may assume the
form of an elongated tube, and which are then known as the con
THE FEMALE GENITAL ORGANS. 347
stricted tubes of Pfliiger. The fourth, fifth, and possibly the third types are further divided by connective-tissue septa, until they finally form distinct and typical follicles (Schottlander, 91, 93).
In the adult ovary true egg tubes are no longer developed. Isolated imaginations of the germinal epithelium sometimes occur, but apparently lead merely to the formation of epithelial cysts (Schottlander). The theories as to when the formation of new epithelial nests or follicles ceases are, however, very conflicting, some authors believing that cessation takes place at birth, others that it continues into childhood and even into middle age.
The typical primitive follicle consists of a relatively large eggcell surrounded by a single layer of smaller cubical or cylindric follicular cells. The growth of the follicle takes place by means of mitotic division in the follicular cells and increase in size of the ovum. The egg-cell is soon surrounded by several layers of cells, and gradually assumes an eccentric position in the cell complex. At a certain distance from the ovum and nearly in the center of the follicle one or more cavities form in the follicular epithelium. These become confluent, and the resulting space is filled by a fluid derived, on the one hand, from a process of secretion and, on the other hand, from the destruction of some of the follicular cells. The cavity is called the antrum of the follicle, and such a follicle has received the name of Graafian follicle. Its diameter varies from 0.5 to 6 mm. The follicle increases in size through cell-proliferation, the cavity increasing and gradually inclosing the egg together with the follicular cells immediately surrounding it, although the latter always remain connected with the wall of the vesicle at some point. The egg now lies imbedded in a cell-mass, the discus proligerus, which is composed of follicular epithelium, and projects into the follicular cavity. The follicular epithelium forming the wall of the cavity is known as the stratum granulosum, the cavity as the antrum, and the fluid which it contains as the liquor folliculi. Those follicular cells which immediately surround and rest upon the ovum are somewhat higher than the rest and constitute the egg epithelium, or corona radiata.
During the growth of the follicle the connective tissue surrounding it becomes differentiated into a special envelope, called the tJicca folliculi. In it two layers may be distinguished the outer, the tunica externa, consisting of fibrous connective tissue, is continuous with the inner, or tunica interna, rich in blood-vessels and cellular elements. The follicle gradually extends to the surface of the ovary, at which point it finally bursts (see below), allowing the ovum to escape into the body cavity and thus into the oviduct.
During the growth and development of the ovarian follicles the ova undergo certain changes of size and structure which may receive further consideration. These have been described for the human ovary by Nagel (96), whose account will here be followed. The
Fig. 280.
Figs. 277, 278, 279, and 280. From sections of cat's ovary, showing ova and follicles in different stages of development ; X 22 5 a i a > a -> a > Germinal spots ; />, i>, b, 6, germinal vesicles ; t, c, c, c, ova ; </, d, d, zonx pellucidse ; e, e, e, e, corona radiata ; f,f,f,f, tbecse folliculorum ; g, beginning of formation of the cavity of the follicle.
348
THE FEMALE GENITAL ORGANS.
349
ova of the primitive or primordial follicles attain a size (in fresh tissue teased in normal salt solution) varying from 48 /* to 69^. They possess a nucleus varying in size from 20 fi to 32^, presenting a doubly contoured nuclear membrane, and containing a distinct chromatin network with a nucleolus and several accessory nucleoli. The protoplasm shows a distinct spongioplastic network containing a clear hyaloplasm. The primitive ova, until they undergo further development, retain this size and structure, irrespective of the age of the individual. They are numerous in embryonic life and early childhood, always found during the ovulation period, but not
Fig. 281. Transverse section through the cortex of a human ovary ; X 5 : ^
Tunica albuginea ; ep, follicular epithelium, zona granulosa ; y^primordial follicles ; ov,
ovum in the discus proligerus ; the, thecaexternafolliculi ; thi, theca interim folliculi with
blood-vessels (Sobotta, "Atlas and Epitome of Human Histology").
observed in the ovaries of the aged. Changes in the size and structure of the ova accompany the proliferation of the follicular cells in the growing follicles. As soon as the follicular cells of a primitive follicle proliferate, as above described, the ovum of the follicle increases in size until it has attained the size of a fully developed ovum. The zona pellucida now makes its appearance, and after this has reached a certain thickness, yolk granules (deutoplastic granules) develop in the protoplasm of the ovum. In a fully developed Graafian follicle the ovum presents an outer clearer protoplasmic zone and an inner fine granular zone containing yolk
35O THE GENITO-URINARY ORGANS.
granules ; in the former lies the germinal vessel. Between the protoplasm of the ovum and the zona pellucida is found a narrow space known as the perivitelline space. The germinal vesicle (nucleus), which is usually of spheric shape, possesses a doubly contoured membrane and a large germinal spot (nucleolus), which shows ameboid movements.
The origin of the zona pellucida has not as yet been fully determined. It probably represents a product of the egg epithelium, and may be regarded in general as a cuticular formation of these cells. At all events it contains numerous small canals or pores into which the processes of the cells composing the corona radiata extend. These processes are to be regarded as intercellular bridges (Retzius, 90) ; and, according to Palladino, they occur not only between the ovum and the corona radiata, but also between the follicular cells themselves. In the ripe human ovum the pores are apparently absent (Nagel), and it is very probable that they have to do with the passage of nourishment to the growing egg. Retzius believes that the zona pellucida is derived from the processes of the cells composing the corona radiata, which at first interlace and form a network around the ovum. Later, the matrix of the membrane is deposited in the meshes of the network, very probably by the egg itself.
Further developmental changes are, however, necessary before a fully developed ovum (ripe ovum) may be fertilized. These are grouped under the head of maturation of the ovum. They have in part been described in a former section (p. 71), but may receive further consideration at this time. During maturation the chromosomes are reduced in number, so that the matured ovum presents only half the number found in a somatic cell of the same animal. The manner in which this reduction takes place has been described for many invertebrates and vertebrates, and in all ova studied with reference to this point essentially the same phenomena have been observed. In this account we shall follow the process as it occurs in the Copepoda (Riickert, 94).
During the period of growth the cells composing the last generation of oogonia (primitive ova) increase in size, and are then known as " oocytes " (the ripe ova). These then undergo mitotic division, and in each a spirem is formed which divides into 12 chromosomes, and not into 24 as in the case of the somatic cells. These 12 chromosomes split longitudinally, so that the germinal vesicle is seen to contain 12 pairs of chromosomes, or daughter loops. By this process the oogonia have become egg mother cells (O. Hertwig, 90) or oocytes of the first order. The loops now begin to shorten and each soon divides crosswise into two equal rods, thus giving rise to 12 groups of 4 chromosomes, or 12 tetrads. The mother cell now divides into 2 unequal parts, the process consisting in a distribution of the rods composing the tetrads in such a
THE FEMALE GENITAL ORGANS.
351
way that the pairs of rods derived from one set of daughter loops pass to the one daughter cell, and those derived from the other set to the second daughter cell. In this manner are formed the large egg daughter cells (O. Hertwig) or oocytes of the second order, and a smaller cell, the first polar body. From this it is seen that the daughter cell still retains 12 pairs of rods. A second unequal division immediately follows without a period of rest, but in this case the corn
Fig. 282. Schematic representation of the behavior of the chromatin during the maturation of the ovum (from Riickert, 94). Instead of 12 chromosomes we have drawn, for the sake of simplicity, only four : a, a, a, First, and (b) second polar body.
ponent parts of the pairs of rods are so divided that each separate rod moves away from its fellow, although they both originated from the same daughter loop. In this manner a cell of the third generation is formed, the oocyte of the third order, or mature ovum, as well as a second polar body. The second division in the period of maturation is peculiar in that here daughter chromosomes are
35 2 THE GENITOURINARY ORGANS.
formed, not by a longitudinal splitting of the chromosomes, but by a transverse division.
In the process of development of the ova, three periods are therefore distinguishable. The first, or period of proliferation, represents a stage of repeated mitotic division in the oogonia, during which the latter become gradually reduced in size. In the second, or period of growth, the oogonia increase in size and are then ready for the third, or period of maturation. In the latter, by means of a modified double mitotic division, uninterrupted by any resting stage, the matured ovum and the polar bodies are formed. These several periods are represented in figure 283.
The manner in which the fully developed Graafian follicle
Primordial egg-cell.
/otic division. \ / (The number of genera tions is much larger than here represented!)
I Germinal zone.
- Zone of mitotic
S Zone of growth.
Oocyte I. order.
Oocyte II. order. ^^^ v I. P. B. f Zone of maturation.
Matured ovum.
K _ f
II. P.B.
Fig. 283. Scheme of the development and maturation of an ascaris ovum (after Boveri) : P. B., Polar bodies. (From " Ergebn. d. Anat. u. Entw.," Bd. I.)
bursts and its ovum is freed is still a subject of controversy ; the following may be said regarding it : By a softening of the cells forming the pedicle of the discus proligerus, the latter, together with the ovum, are separated from the remaining granulosa, and lie free in the liquor folliculi. At the point where the follicle comes in contact with the tunica albuginea of the ovary, the latter, with the theca folliculi, becomes thin, and in this region, known as the stigma, the blood-vessels are obliterated and the entire tissue gradually atrophies ; thus a point of least resistance is formed which gives way at the slightest increase in pressure within the follicle, or in its neighborhood.
THE FEMALE GENITAL ORGANS. 353
The part of the Graafian follicle which remains after the ovum has been released forms a structure known as the corpus luteum, a structure which passes through certain developmental stages and then undergoes degeneration. The regressive metamorphosis is much slower in a corpus luteum whose ovum has been fertilized and is in process of further development than in those whose ova have not been impregnated ; the former is known as the corpus luteum verum, the latter as the corpora lutea spuria. There is as yet difference of opinion as to the mode of development of the corpora lutea, certain observers maintaining that the cells ofthezona granulosa contribute largely to the development of these structures, while others trace their origin to the cells of the theca interna. In this account we shall follow Sobotta, whose careful observations on the development of the corpora lutea of the mouse and rabbit support strongly the former view. According to this observer, the walls of the Graafian follicle collapse after its rupture. The cells of the follicular epithelium, which remains within the collapsed follicle, hypertrophy, the cells attaining many times their original size. As the epithelial cells enlarge, a yellowish pigment known as Lutein makes its appearance. The cells are now designated as lutein cells. At the same time the vascular connective tissue of the inner thecal layer penetrates between the hypertrophied epithelial cells in the shape of processes accompanied by leucocytes.
The structure' which thus develops is known as the corpus luteum. On the rupture of the follicle hemorrhages often take place on account of the laceration of the blood-vessels. The remains of such hemorrhages are found in the form of hematoidin crystals.
After a variable time the corpora lutea degenerate ; in this regressive metamorphosis the epithelial cells (lutein cells) undergo fatty degeneration, and the connective tissue trabeculae become atrophied. Each corpus luteum is thus changed into a corpus albicans, which in turn is absorbed, and in its place there remains only a connective tissue containing very few fibers.
Not all of the eggs and follicles reach maturity ; very many are destroyed by a regressive process known as atresia of the follicles. This process may begin at any stage, even affecting the primitive ova while still imbedded in the germinal epithelium first attacking the egg itself and later the surrounding follicular epithelium, although in both the degenerative process is identical. The germinal vesicle and the nuclei of the follicular cells usually undergo a chromatolytic degeneration, although they sometimes disappear without apparent chromatolysis (direct atrophy), while the cell-bodies are generally subjected to a fatty degeneration or may even undergo what is known among pathologists as an albuminous degeneration i. e., one characterized by granulation and showing no fat reaction but numerous reactions such as are observed where albumin is present. These two forms of metamor23
354 THE GENITOURINARY ORGANS.
phosis result in a liquefaction of the cell-body, and finally lead to a hyaline swelling, which renders the substance of the cell homogeneous. The zona pellucida softens, increases in volume, becomes wrinkled, and after some time is absorbed. A further stage in the regressive process consists in the formation of scar tissue, as in the case of the corpus luteum. Here leucocytes accompany the proliferation from the tunica interna of the theca folliculi, and assist in absorbing the products of degeneration, the result being a connective-tissue scar (vid. G. Ruge, and Schottlander, 91, 93).
The blood-vessels of the ovary enter at the hilum and branch in the medullary substance of the ovary. From these medullary vessels branches are given off which penetrate the follicular zone, giving off branches to the follicles and terminating in a capillary network in the tunica albuginea (Clark, 1900). The relations of the branches to the follicles are such that in the outer layer of the theca folliculi the vessels form a network with wide meshes while the inner layer contains a fine capillary network. The veins are of large caliber and form a plexus at the hilum of the ovary.
The lymphatics of the ovary are numerous. They begin in clefts in the follicular zone, which unite to form vessels lined by endothelial cells in the medulla. They leave the ovary at the hilum.
The nerves accompany and surround the blo*od-vessels, while very few nerve-fibers penetrate into the theca folliculi ; those doing so form a network around the follicle and end often in small nodules without penetrating beyond the theca itself. Ganglion cells of the sympathetic type also occur in the medulla of the ovary near the hilum (Retzius, 93 ; Riese, Gawronsky).
3. THE FALLOPIAN TUBES, UTERUS, AND VAGINA.
The Fallopian tubes or ova ducts consist of a mucous membrane, muscular coat, and peritoneal covering.
The mucous membrane presents a large number of longitudinal folds which present numerous secondary folds which frequently communicate with one another. Very early in the development four of these folds are particularly noticeable in the isthmus ; these may also be recognized at times in the adult. These are the chief folds, in contradistinction to the rest, which are known as the accessory folds (Frommel). The accessory folds are well developed in the isthmus, and are here so closely arranged that no lumen can be seen with the naked eye. The epithelium lining the tubes is composed of a single layer of ciliated columnar cells which entirely cover the folds as well as the tissue between them. Glands do not occur in the oviducts, unless the crypts between the folds may be considered as such. The mucosa beneath the epithelium contains relatively few connective-tissue
THE FEMALE GENITAL ORGANS.
355
fibers, but numerous cellular elements. In the isthmus it is compact, but in the ampulla and infundibulum its structure is looser. The mucosa contains a few nonstriated muscle-fibers, which have a longitudinal direction and extend into the chief folds, but not into the accessory folds.
External to the mucosa is found the muscular coat, consisting of an inner circular and an outer and thinner longitudinal layer consisting of bundles of nonstriated muscular tissue separated by connective tissue and blood-vessels. The longitudinal layer is imperfectly developed in the ampulla and may be entirely absent in the infundibulum. The peritoneal layer consists of a loose connective tissue covered by mesothelium.
Mucosa.
Crypt. J
_ Crypt.
Fig. 284. Section of oviduct of young woman. To the left and above are two enlarged ciliated epithelial cells from the same tube ; X I 7
The ova ducts have a rich blood-supply. The terminal branches
of the arteries pass into the primary and secondary folds of the
mucosa, where they form capillary plexuses under the epithelium.
The blood is returned by means of a well-developed venous plexus.
The lymphatic vessels have their origins in the folds of the mucosa.
Nerve-fibers have been traced to the musculature and to the lining
epithelial cells.
The uterus is composed of a mucous, a muscular, and a peritoneal coat.
The mucosa of the body of the uterus and cervix is lined by a single layer of columnar ciliated epithelial cells ; these are some
3 $6 THE GENITO-URINARY ORGANS.
what higher in the cervix than in the corpus. Barfurth (96) has found intercellular bridges between the cells of the uterine epithelium in the guinea-pig and rabbit. In the cervix of the virgin the ciliated columnar epithelium extends as far as the external os, at which point this usually changes to a stratified squamous epithelium. In multiparae the squamous epithelium extends into the cervical canal and may be found, with occasional exceptions (islands of ciliated epithelium), throughout its entire lower third. This arrangement is subject to considerable variation, so that even in children the lower portion of the cervical canal may sometimes be lined by stratified epithelium. Recent investigations have established the fact that in both the uterus and oviducts the general direction of the wave-like ciliary motion is toward the vagina (Hofmeier). In the body of the uterus the mucosa is composed of a reticular connective tissue consisting of relatively few connective-tissue fibers and branched connective-tissue cells arranged in the form of a network, in the meshes of which are found lymphocytes and leucocytes. Under low magnification the mucosa presents more the appearance of adenoid tissue than of areolar connective tissue. The mucosa of the cervix is somewhat denser, containing more fibrous tissue. In the cervical canal the mucosa of the anterior and posterior walls is elevated to form numerous folds, extending laterally from larger median folds. These folds are known as the plica palmatce.
The mucosa of the body of the uterus and of the cervix contains numerous glands, the uterine and cervical glands. The uterine glands are branched tubular in type, and extend through the mucosa and certain ones may even extend for a short distance into the muscular layer. They are lined by ciliated columnar epithelium, resting on a basement membrane. The cervical glands are larger and more branched than those of the body of the uterus, and belong to the type of tubulo-alveolar glands ; they have a mucous secretion. The glands and crypts extend as far as the external os. In the mucous membrane of the cervical region we find peculiar closed sacs of varying size lined by simple cylindric epithelium, the socalled ovula Nabothi, which probably represent cystic formations (yid. A. Martin).
Three layers of muscular tissue are to be seen both in the corpus and cervix uteri an inner longitudinal, a middle nearly circular, in which the principal blood-vessels are found, and an outer longitudinal. The inner and outer layers are known respectively from their position as the stratum mucosum and stratum serosum, the middle and more vascular as the stratum vasculosum. As compared with the middle, the inner and outer muscle layers are poorly developed. The complicated conditions found in the uterine musculature can be better understood if some attention be paid to its origin. The circular layer should be regarded as the original musculature of the Miillerian ducts. The outer longitudinal layer develops later, and is derived from the musculature of the broad
THE FEMALE GENITAL ORGANS.
357
ligament. Between these two are the large vessels accompanied by a certain amount of muscular tissue a condition which persists throughout life in the carnivora. In man the blood-vessels penetrate into the circular musculature and only appear later in the inner muscular layer. A true muscularis mucosse is not present in the human uterus (Sobotta, 91).
The serous or peritoneal layer consists of a layer of mesothelial cells and submesothelial connective tissue.
The uterus derives its blood supply from the uterine and ovarian arteries, which enter from the broad ligament through its lateral portion. These vessels pass to the stratum vasculosum of the muscular layer, where they branch repeatedly, some of the branches
Uterine
epithelium.
g Gland.
>- Mucosa.
Fig. 285. From uterus of young woman ; X 34- (From a preparation by Dr.
J. Amann.)
entering the mucosa, where they form capillary networks surrounding the glands and a dense capillary network situated under the uterine epithelium. The veins form a venous plexus in the deeper portion of the mucosa, especially well developed in the cervix and os uteri. From this plexus the blood passes to a second welldeveloped venous plexus situated in the stratum vasculosum of the muscular layer, whence the blood passes to the plexus of uterine and ovarian veins.
The lymphatics begin in numerous clefts in the uterine mucosa ;
358
THE GENITOURINARY ORGANS.
from here the lymph passes by way of lymph-vessels to the muscular coat, between the bundles of which are found numerous lymph-vessels especially in the middle or vascular layer. These lymph-vessels terminate in larger vessels found in the subserous connective tissue.
The uterus receives numerous medullated and nonmedullated nerves. The latter terminate in the muscular layers. Medullated fibers have been traced into the mucosa, where they form plexuses under the epithelium, from which branches have been traced between the epithelial cells and between the gland cells. In the course of the nerves ganglion cells of the sympathetic type have been observed.
Fig. 286. From section of human vagina.
In the vagina we distinguish also three coats the mucous membrane, the muscular layer, and the outer fibrous covering.
The epithelium of the mucous membrane is of the stratified squamous type, and possesses, as usual, a basal layer of cylindric cells. The mucosa of the vagina consists of numerous connectivetissue fibers mingled with a number of exceptionally coarse elastic fibers. Papillae containing blood-vessels are present everywhere except in the depressions between the columnar rugarum. It is generally stated that the vagina has no glands, but according to the observations of von Preuschen and C. Ruge, a few isolated glands occur in
THE FEMALE GENITAL ORGANS.
359
the vagina. They are relatively simple in structure, form irregular tubes, and are lined by ciliated columnar epithelium. The excretory ducts are lined by stratified squamous epithelium. Diffuse adenoid tissue is met with in the mucosa, which sometimes assumes the form of lymphatic nodules.
The muscular coat, which in the lower region is quite prominent, may be separated indistinctly into an outer longitudinal and an inner circular layer ; the latter is, as a rule, poorly developed, and may be entirely absent. The muscular coat is especially well developed anteriorly in the neighborhood of the bladder.
Fig. 287. From section of human labia minora.
The outer fibrous layer consists of dense connective tissue loosely connected with the adjacent structures.
At its lower end the vagina is partially closed by the hymen which must be regarded as a rudiment of the membrane which in the embryo separates the lower segment of the united Miillerian ducts from the ectoderm of the sinus urogenitalis. Accordingly, the epithelium on the inner surface of the hymen partakes of the character of the vaginal epithelium ; that on the outer surface resembling the skin in structure (G. Klein).
360 THE GENITO-URINARY ORGANS.
The epithelium of the vestibulnm gradually assumes the characteristics of the epidermis ; its outer cells lose their nuclei and sebaceous glands occur here and there in the neighborhood of the urethral orifice and on the labia minora. Hair begins to appear on the outer surface of the labia majora.
The clitoris is covered by a thin epithelial layer, resembling the epidermis. This rests on a fibrous-tissue mucosa having numerous papillae, some of which contain capillaries, others special nerveendings. In the clitoris of the adult no glands are found. The greater portion of the clitoris consists of cavernous tissue, homologous to the corpora cavernosa of the penis ; the corpus spongiosum is not present in the clitoris.
The glands of Bartholin, the homologues of the glands of Cowper in the male, are mucous glands situated in the lateral walls of the vestibule of the vagina. The terminal portions of their ducts are lined by stratified squamous epithelium.
Free sensory nerve-endings, with or without terminal enlargements, have been demonstrated in the epithelium of the vagina (Gawronski). The sensory nerve-fibers form plexuses in the mucosa, and lose their medullary sheaths as they approach the epithelium. Sympathetic ganglia are met with along the course of these nerves, and nonmedullated nerves terminate in the involuntary muscular tissue of the vaginal wall.
In*the connective-tissue papillae and in the deeper portions of the mucosa of the glans clitoridis are found, besides the ordinary type of tactile corpuscles and the spherical end-bulbs of Krause, the socalled genital corpuscles (see p. 171). Numerous Pacinian corpuscles have been observed in close proximity to the nerve-fibers of the clitoris and the labia minora.
In varying regions of the medullary substance of the ovary, but more usually in the neighborhood of the hilum, there occur irregular epithelial cords or tubules provided with columnar epithelium, ciliated or nonciliated, which constitute the paroophoron. These are the remains of the mesonephros, and are continuations of that rudimentary organ the epoophoron of similar structure which lies within the broad ligament. The separate tubules of the epoophoron communicate with the duct of Gartner (Wolfifian duct), which in the human being is short, ends blindly, and never, as in certain animals, opens into the lower portion of the vagina. These derivatives of the primitive kidney consist of blindly ending tubules of varying length lined by a ciliated epithelium, the cells of which are often found in process of degeneration.
The hydatids of Morgagni are duplications of the peritoneum.
THE MALE GENITAL ORGANS. 361
D. THE MALE GENITAL ORGANS.
J. THE SPERMATOZOON.
The semen, or sperma, is a fluid that, as a whole, consists of the secretion of several sets of glands in which the sexual cells, the spermatosomes, or spermatozoa, which are formed in the testes, are suspended.
We shall first consider the structure of the typical adult spermatosome, taking up consecutively its component parts. Three principal parts may be distinguished the head, the middle piece, and the tail or flagellnm. The round or oval body of the head terminates in a lanceolate extremity. The former consists of chromatin, and is most intimately associated with the phenomenon of fertilization. The middle piece, which is attached to the posterior end of the head, is composed of a protoplasmic envelop which surrounds a portion of the so-called axial thread. The latter is enlarged anteriorly just behind the head to form the terminal nodule, which fits into a depression in the head. From the middle piece on, the axial thread
Fig. 288. Diagram showing the general characteristics of the spermatozoa of
various vertebrates : a, Lance ; b, segments of the accessory thread ; c, accessory
thread ; d, body of the head ; e, terminal nodule ; f, middle piece ; g, marginal thread ;
h, axial thread ; i, undulating membrane ; k, fibrils of the axial thread ; /, fibrils of the
marginal thread ; m, end piece of Retzius ; ;/, rudder-membrane.
is continued into the tail of the spermatozoon, and is here surrounded by a transparent substance the sheatJi of the axial thread. The envelop is lacking at the posterior extremity of the tail, where the axial thread extends for a short distance as a naked filament called the end-piece of Retzius. From the middle piece a still finer thread is given off", the marginal thread, which extends at a certain distance from the axial thread as far as the end-piece of Retzius. In its course it crosses and recrosses the axial thread at various points, and may even wind around it in a spiral manner. In all instances it is connected with the sheath of the axial thread by a delicate membrane the undulating membrane. Another and still more delicate filament the accessory thread runs parallel with the axial thread along the surface of its sheath and terminates at a certain distance from the end-piece of Retzius. Near the extremity of the flagellum and immediately in front of the end-piece is another and shorter membrane, the rudder membrane, which is continuous with the undulating membrane. Maceration reveals a fibrillar
362
THE GENITOURINARY ORGANS.
I- a
structure of both the axial and marginal threads (Ballowitz), while the accessory thread is separated into a number of short segments. In mammalia, and especially in man, the spermatozoa seem to be" more simply constructed. Here the head is pyriform, and somewhat flattened, with a slight ridge along the depression at either side of its anterior thinner portion (Fig. 289). In some mammalia (mouse), the head is provided with a socalled cap, which corresponds to the lance previously mentioned. The middle piece is relatively long and shows a distinct crossstriation, which may be attributed to its spiral structure. Here also the middle piece is traversed by the axial thread, which ends at the head in a terminal nodule, and may be separated as in other mammalia into a number of fibrils. Some years ago Gibbes described an undulating membrane in the human spermatozoon, an observation which was confirmed by W. Krause (81). The head of the .human spermatosome is from 3 /j. to 5 [i long, and
from 2 u to 3 u in breadth ; the middle piece Fig. 289. Human ' J '
spermatozoa. The two is 6 // long and I fj. in breadth ; the tail is from
at the left after Retzius 40 // to 60 /J. long, and the end-piece 6 fj. long.
extreme left ^ seen* in ^he spermatozoa are actively motile, a phe profile; the other in nomenon due to the flagella, which give them
surface view; the one a S pi ra 1 boring motion. They are character at the right is drawn as ,
described by Jensen -. a, lz ed by great longevity and are very resistant Head ; l>, terminal nod- to the action of low temperatures (vid. Pier ule; c, middle piece; gol g \ j n SQme spedes o f bat the Spera, tail ; e, end-piece of . L r
Retzius. matozoa penetrate into the oviduct of the
female in the fall, but do not contribute to impregnation until the spring, when the ova mature. (For the structure of the spermatosomes see Jensen, Ballowitz.)
2. THE TESTES.
The testis is inclosed within a dense fibrous capsule, the tunica albuginea, about one-sixteenth of an inch in thickness, and surrounded by a closed serous sac, derived from the peritoneum during the descent of the testes, and therefore lined by mesothelial cells. This serous sac the tunica vaginalis consists of a visceral layer attached to the tunica albuginea, and a parietal layer which blends with the scrotum. The cavity contains normally a small amount of serous fluid. On the inner surface of the tunica albuginea is found a thin layer of loose fibrous tissue containing blood-vessels the tunica vasculosa. The tunica albuginea is thickened in its
THE MALE GENITAL ORGANS.
posterior portion to form the mediastinum testis, or the corpus Highmori, which projects as a fibrous-tissue ridge for a variable distance into the substance of the testis. The gross structure of the testis is best seen in a sagittal longitudinal section. Even a low magnification will show that the testis is composed of lobules. These are produced by septa which extend into the substance of the organ and are derived from the investing tunics of the testis and diverge in a radiate manner from the mediastinum testis. The lobules are of pyramidal shape, with their bases directed toward the capsule and their apices toward the mediastinum. They consist principally of the seminiferous tubules, whose transverse, oblique, and longitudinal
Lobule of testis. Tunica albuginea.
_Caput epididymidis.
Corpus Highmori and rete testis.
Blood-vessel.
Tubuli recti.
J<? I /
', cWr Vasepididymidis.
Fig. 290. Longitudinal section through human testis and epididymis. The light areas between the lobules are the fibrous-tissue septa of the testis ; X 2
sections may be observed in sections of the testis. When isolated, these tubules are seen to begin in the testis as closed canals, which are closely coiled upon each other (convoluted tubules) and describe a tortuous course, until they finally reach the corpus Highmori. Immediately before they reach the latter, the convoluted tubules change into short, straight and narrow segments' the straight tubules, or tubuli recti. Within the corpus Highmori, all the straight tubules of the testis unite to form a tubular network the rete testis (Haller).
From this network about fifteen tubules the vasa efferentia
364 THE GENITOURINARY ORGANS.
arise. The latter, at first straight, soon begin to wind in such a manner that the various convolutions of each canal form an independent system, invested by a fibrous sheath of its own coni vasculosi Halleri. These lobules constitute the elements of the globus major of the epididymis. In cross-section the vasa efferentia are seen to be stellate in shape. The vasa efferentia gradually unite to form one canal the vas epididyntidis. This is markedly convoluted and is situated in the body and tail of the epididymis itself.
The epithelium of the convoluted seminiferous tubules consists of sustentacular cells (cells or columns of Sertoli) and of spermatogenic elements. The former are high, cylindric structures (see below), the basilar surfaces of which are in contact. They do not form a continuous layer, but their basal processes are interwoven to form a superficial network surrounding the epithelium of the
Fig. 291. Fig. 292.
Sustentacular cells (cells of Sertoli) of the guinea-pig (chrome-silver method). Figure 291, surface view of the seminiferous tubules ; figure 292, profile view ; X 22 : a, Basilar surface of a cylindric sustentacular cell ; i>, flattened sustentacular cell ; <-, <r, depressions in the sustentacular cells due to pressure from the spermatogenic cells ; d, basilar portion of sustentacular cells.
seminiferous tubules. (Fig. 292.) In the meshes of the reticulum are deposited numbers of plate-like cells, which lie in contact with the basement membrane and also represent sustentacular elements (vid. Merkel, 7 1 ).
Between the sustentacular cells are found from four to six rows of cells, possessing relatively large nuclei, rich in chromatin, and derived from cells of the deeper strata by mitotic cell division. The epithelium of the convoluted portion of the seminiferous tubules is, therefore, a stratified epithelium. The cells of this epithelium present various peculiarities according to their stage of development, and will be considered more fully in discussing spermatogenesis. Externally, the walls of the convoluted tubules are limited by a single layer or several layers of spindle-shaped, epithelioid cells. A basement membrane is present, but very thin, and in some cases
THE MALE GENITAL ORGANS.
hardly capable of demonstration. The convoluted tubules are separated from each other by a small amount of connective tissue, in which, in addition to the vessels, nerves, etc., are found peculiar groups of large cells containing large nuclei, and known as interstitial cells. Nothing definite is known regarding the significance of these cells ; but they are probably remains of the Wolffian body. Reinke (96) found repeatedly crystalloids of problematic significance in the interstitial cells of the normal testis.
The stratified epithelium of the convoluted tubules changes in
- .'":: ^^- >::*
Fig. 293. From section of human testis, showing convoluted seminiferous
tubules.
the tubuli recti to an epithelium consisting of a single layer of short columnar or cubical cells resting on a thin basement membrane.
The canals of the rete testis (Haller) are lined by nonciliated epithelium, which varies in type from flat to cubical. Communicating with the rete testis is a blind canal, the vas aberrans of the rete testis, lined with ciliated epithelium.
The vasa efferentia are lined partly by ciliated columnar and partly by nonciliated cubical epithelium. The two varieties form groups which alternate, giving rise to nonciliated depressions, which represent gland-like structures (Schaffer, 92), but do not
366
THE GENITOURINARY ORGANS.
cause corresponding evaginations of the mucosa. The mucosa, which consists of fibrous connective tissue, contains flattened endothelioid cells, which resemble nonstriated muscle-cells. The latter are found only at the end of the vasa efferentia, just before reaching the vas epididymidis.
Fig. 294. Section through human vasa efferentia : a, Glands ; b, ciliated epithelium ;
f, glandular structure ; d, connective tissue.
Fig. 295. Cross-section of vas epididymidis of human testis.
The vas epididymidis is lined by stratified ciliated columnar epithelium, resting on a thin mucosa, outside of which there is found an inner circular and an outer, though thin and not continuous, longitudinal layer of nonstriated muscular tissue.
An aberrant canaliculus also communicates with the vas epididymidis, and is here known as the vas aberrans Halleri. Num
THE MALE GENITAL ORGANS.
367
bers of convoluted and blindly ending canaliculi are frequently found imbedded in the connective tissue around the epididymis. These constitute the paradidymis, or organ of Giraldes.
The blood-vessels of the testis spread out in the corpus Highmori and in the tunica vasculosa of the connective-tissue septa and of the tunica albuginea, their capillaries encircling the seminal tubules in well-marked networks.
The lymphatic vessels begin in clefts in the tunica albuginea and in the connective tissue between the convoluted tubules. They converge toward the corpus Highmori and pass thence to the spermatic cord.
Retzius (93) and Timofeew (94) have described plexuses of nonmedullated, varicose nerve-fibers surrounding the bloodvessels of the testis. From such plexuses single fibers, or small bundles of such, could be traced to the seminiferous tubules, about which they also form plexuses. Such
Fig. 296. Section of dog's testis with injected blood-vessels (low power) : a, Seminiferous tubule ; b, connective-tissue septum ; c, bloodvessel.
fibers have not been traced into the epithelium lining the tubules. In the epididymis Timofeew found numerous sympathetic ganglia, the cellbodies of the sympathetic
neurones of which were surrounded by pericellular plexuses. In the wall of the vas epididymidis and the vasa efferentia were observed numerous varicose nerve-fibers, arranged in the form of a plexus, many of which seemed to terminate on the nonstriated muscle cells found in these tubes. Some of the nerve-fibers were traced into the mucosa, but not into its epithelial lining.
3. THE EXCRETORY DUCTS.
The vas deferens possesses a relatively thick muscular wall, consisting of three layers, of which the middle is circular and the other two longitudinal. The subepithelial mucosa is abundantly supplied with elastic fibers and presents longitudinal folds. The lining epithelium is in part simple ciliated columnar and in part stratified ciliated columnar, with two rows of nuclei. The cilia are, however, often absent, beginning with the lower portion of the vas epidi
368
THE GENITOURINARY ORGANS.
dymidis. According to Steiner, the epithelium of the vas deferens varies. It may be provided with cilia in the lower segments, or it may even be similar to that found in the bladder and ureters.
The inner muscular layer is wanting in the ampulla of the vas deferens ; here the epithelium is mostly simple columnar and pigmented. Besides the folds, there are also evaginations and tubules which sometimes form anastomoses structures which may be regarded as glands.
The seminal vesicles are also lined, at least when in a distended condition, by simple, nonciliated columnar epithelium containing yellow pigment. In a collapsed condition the epithelium is pseudostratified, with two or even three layers of nuclei. The arrangement of the epithelial cells in a single layer would therefore seem to be the result of distention. The mucous membrane shows
Epithelium.
Outer longitudinal
muscular
layer.
Fig. 297. Cross-section of vas deferens near the epididymis (human).
numerous folds, which, in the guinea-pig for instance, present a delicate axial connective -tissue stroma. Besides scanty subepithelial connective tissue, the seminal vesicles are provided with an inner circular and an outer longitudinal layer of muscle-fibers. Spermatozoa are, as a rule, not met with in the seminal vesicles.
The epithelium of the ejaculatory ducts is composed of a single layer of cells ; the inner circular muscle-layer is very poorly developed. In the prostatic portion of the ejaculatory ducts the longitudinal muscle-layer mingles with the musculature of the prostate and loses its individuality. The ejaculatory ducts empty either directly into the urethra at the colliculus seminalis, or indirectly into the prostatic portion of the urethra through the vesicula prostatica.
1\i& prostate is a compound branched tubulo-alveolar gland. Its
THE MALE GENITAL ORGANS.
369
capsule consists of dense layers of nonstriated muscle-fibers, connective tissue, and yellow elastic fibers. Processes and lamellae composed of all these elements extend into the interior of the gland, converging toward the base of the colliculus seminalis. Between the larger trabeculae are situated numerous glands, consisting of large,
Fig. 298. Cross-section of wall of seminal vesicle, showing the folds of the
mucosa (human).
Fig. 299. From section of prostate gland of man.
irregular alveoli, separated by fibromuscular septa and trabeculas. The alveoli are lined by simple columnar epithelium, the inner portion of the cells often showing acidophile granules. Now and then the alveoli present a pseudostratified epithelium, with two rows of nuclei (Rudinger, 83). A basement membrane, although 24
3/O THE GENITOURINARY ORGANS.
present, is difficult to demonstrate and consists of a network of delicate connective-tissue threads, as was shown by Walker. The numerous excretory ducts, lined by simple columnar epithelium, become confluent and form from 1 5 to 30 collecting ducts which empty, as a rule, either at the colliculus seminalis or into the sulcus prostaticus. Near their terminations the larger ducts are lined by transitional epithelium similar to that lining the prostatic portion of the urethra.
In the alveoli of the glands, peculiar concentrically laminated concrements are found, known as prostatic bodies or concretions (corpora amylacea). They are more numerous in old men, but are found in the prostates of young men and also of young boys. The secretion of the prostate (succus prostaticus) is not mucous in character, but resembles a serous secretion and has an acid reaction. The vesicula prostatica (sinus pocularis) is lined by stratified epithelium, consisting of two layers of cells and provided with a distinct cuticular margin upon which rest cilia. In its urethral region occur short alveolar glands.
The glands of Cowper are branched tubular alveolar glands, the alveoli being lined by mucous cells. The smaller excretory ducts, lined by cubical epithelium, unite to form two ducts, one on each side of the urethra ; these are I ^ inches long, and are lined by stratified epithelium consisting of two or three layers of cells.
The blood-vessels of the prostate ramify in the fibromuscular trabeculae and form capillary networks surrounding the alveoli. The veins collecting the blood pass to the periphery of the gland, where they form a plexus in the capsule. The lymphatics begin in clefts in the trabeculae and follow the veins. The terminal branches of the vessels supplying Cowper's glands are, in their arrangement, like those of other mucous glands.
Numerous sympathetic ganglia are found in the prostate under the capsule and in the larger trabeculse near the capsule. The neuraxes of the sympathetic cells of these ganglia may be traced to the vessels and into the trabeculae ; their mode of ending has, however, not been determined. Small medullated nerve-fibers terminate in these ganglia in pericellular baskets. Timofeew has described peculiar encapsulated sensory nerve-endings, found in the prostatic and membranous portions of the urethra of certain mammalia. They consist of the terminal branches of two kinds of nerves, inclosed within nucleated laminated capsules : one large medullated nerve -fiber, after losing its medullary sheath, breaks up into a small number of ribbon-shaped branches with serrated edges, which may pass more or less directly to the end of the nerve-ending or may be bent upon themselves ; and very much smaller medullated nerve-fibers which, after losing their medullary sheaths, divide into a large number of varicose fibers which form a dense network encircling the ribbon-shaped fibers previously mentioned.
The penis consists of three cylindric masses of erectile tissue the two corpora cavernosa, forming the greater part of the penis
THE MALE GENITAL ORGANS.
and lying side by side, and the corpus spongiosum, surrounding the urethra and lying below and between the corpora cavernosa. The two latter are surrounded by a dense connective-tissue sheath, the tunica albuginea. These erectile bodies are surrounded by a thin layer of skin, containing no adipose tissue and no hair-follicles. The corpus spongiosum is enlarged anteriorly to form the glans penis.
The principal substance of the erectile bodies is the so-called erectile tissue : septa and trabeculae, consisting of connective tissue, elastic fibers, and smooth muscle-cells inclosing a system of communicating spaces. These latter may be regarded as venous sinuses, the walls of which, lined by endothelial cells, are in apposition to the erectile tissue. Under certain conditions the venous sinuses are distended with blood, but normally they are in a collapsed state and form fissures which simulate the clefts found in ordinary connective tissue. In other words, there is here such an arrangement of the blood-vessels within the erectile tissue that the circulation may be carried on with or without the aid of the cavernous spaces. The arteries of the corpora cavernosa possess an especially well-developed musculature. They ramify throughout the trabeculas and septa of the erectile tissue and break up within the septa into a coarsely meshed plexus of capillaries. A few of these arteries empty directly into the cavernous spaces. On the other hand, the arteries give off a rich and narrow-meshed capillary network immediately beneath the tunica albuginea. This is in communication with a deeper and denser venous network, which, in turn, gradually empties into the venous sinuses. Aside from these there are anastomoses between the arterial and venous capillaries, which later communicate with the venous network just mentioned. The blood current, regulated as it thus is, may pass either through the capillaries alone, or may divide and flow through both these and the venous sinuses. These conditions explain both the erectile and quiescent state of the penis. The relations are somewhat different in the corpus spongiosum urethrae and in the glans penis. In the corpus spongiosum the arteries do not open directly into the venous spaces, but break up first into capillaries. In the submucosa of the urethra there is found a rich venous plexus. In the glands the arteries end in capillaries which pass over into veins with well-developed muscular walls. The blood is collected by means of the venae emissariae which empty into the vena dorsalis penis and into the venae profundae.
The epithelium of the urethra varies in the several regions. The prostatic portion possesses an epithelium similar to that of the bladder. In the membranous portion, the epithelium may be similar to that found in the prostatic portion, but more often presents the appearance of a pseudostratified epithelium with two or three layers of nuclei. The cavernous region is lined by pseudostratified epithelium, except in the fossa navicularis, where a stratified squamous epithelium is found. Between the fibre-elastic
37 2 THE GENITOURINARY ORGANS.
mucosa and the epithelium there is a basement membrane. There occur in the urethra, beginning with the membranous portion, irregularly scattered epithelial sacculations of different shapes. Some of these show alveolar branching, and are then known as the glands of Littre.
The submucosa of the cavernous portion of the urethra, which contains nonstriated muscle-tissue arranged circularly, is richly supplied with veins, and contains pronounced plexuses communicating with cavernous sinuses, which correspond in general to those of the corpora cavernosa penis.
The glans is covered by a layer of stratified squamous epithelium, often possessing a thin stratum corneum (see Skin). Near the corona of the glans penis there are now and then found small sebaceous glands (see Hair), known as glands of Tyson. The prepuce is a duplication of the skin, the inner surface presenting the appearance of a mucous membrane.
The nerves terminating in the glans penis have recently been studied by Dogiel, who made use of the methylene-blue method in his investigation. He finds Meissner's corpuscles in the connectivetissue papillae under the epithelium, Krause's spheric end-bulbs somewhat deeper in the connective tissue, and the genital corpuscles situated still deeper (see Sensory Nerve-endings). In the epithelium are found free sensory nerve-endings. Pacinian corpuscles have also been found in this region.
4. SPERMATOGENESIS.
In order that the student may obtain an understanding of the complicated process of spermatogenesis we shall give a description of it as it occurs in salamandra maculosa, which of all vertebrate animals presents the phenomena in their simplest and best known form. The student should understand, however, that many of the details here described have not been observed in the testes of mammalia ; and, since the spermatozoa of many of the mammalia are of simpler structure than those of the salamander, the development of the spermatozoa of the former is consequently simpler. It should also be noticed that the general structure of the testes of the salamander differs in some respects from that of the testes of mammalia, as given in the preceding pages.
At first the seminiferous tubules consist of solid cellular cords, and it is only during active production of spermatozoa that a central lumen is formed, in which the spermatosomes then lie. The cells which compose these solid cords may be early differentiated into two classes those of the one class being directly concerned in the production of the spermatosomes ; those of the other appearing to have a more passive role. The cells of the first class the spcrmatogonia, or primitive seminal cells undergo a process of division accompanied by an increase in size. In this way they soon commence to press upon the cells of the second class \\\& follicular o\~ sustentacu
SPERMATOGENESIS.
373
lar cells. The result is that the nuclei of the latter are forced more or less toward the wall of the seminal tubule, while their protoplasm is so indented by the adjacent spermatogonia that the cells assume a flattened cylindric shape presenting indentations and processes on all sides. In this stage the spermatogonia have a radiate arrangement and entirely surround the elongated sustentacular cells. At present three periods are distinguished in the development of the male sexual cells (spermatosomes) from the spermatogonia. The first period embraces a repeated mitotic division of the spermatogonia the period of proliferation. In the second, the spermatogonia, which have naturally become smaller from repeated division, begin to increase in size the period of growth. The third is characterized by a modified double mitotic division without intervening period of rest, and results in the matured spermatozoa the period of maturation, figure 300. During the third period, a very important and significant process takes place the
Primordial sexual cell.
Spermatogonia. ,,
\ \
Spermatocyte I order.
Spermatocytes II o Sperma
Zone of proliferation.
(The generations are
much larger.)
Zone of growth.
Zone of maturation.
Fig. 300. Schematic diagram of spermatogenesis as it occurs in ascaris (after Boveri). ("Ergebn. d. Anat. u. Entw.," Bd. I.)
reduction in the number of chromosomes, so that in the spermatids, the chromosomes are reduced to half the number present in a somatic cell of the same animal. The manner in which this reduction in the number of chromosomes takes place will be described as it occurs in salamandra maculosa.
After the cells composing the last generation of spermatogonia have attained a certain size (period of growth), they undergo karyokinetic division. First, the usual skein or spirem is formed, but instead of dividing into twenty-four chromosomes, as in the somatic cell, the filament of the skein segments into only twelve loops. The cell thus provided with twelve chromosomes now enters upon the period of maturation, and is known as a
374 THE GENITOURINARY ORGANS.
spermatocyte of the first order, or a "mother cell" (O. Hertwig, 90). The division of these cells is heterotypic (vid. p. 70); the chromosomes split longitudinally and in such a way that the division begins at the crown of the loops, extending gradually toward their free ends. In this case the daughter chromosomes remain for some time in contact, so that the metakinetic figure resembles a barrel in shape. Finally, the daughter chromosomes separate and wander toward the poles. As soon as the daughter stars (diaster) are developed, the number of chromosomes is again doubled by a process of longitudinal division. The spermatocyte of the first order thus divides into two spermatocytes of the second order, or daughter cells (O. Hertwig, 90). The nuclei of the daughter cells now contain twenty-four chromosomes, as is the case in the somatic cell, and, without undergoing longitudinal splitting, the daughter chromosomes are distributed to the two nuclei of the spermatids. In other words, the latter contain only twelve chromosomes. The spermatozoa are formed from the spermatids by a rearrangement of the constituent elements of these cells. It may thus be said that even in the stage of the segmenting skein in the mother cells, the spermatocytes of the first degree contain twice as many chromosomes as a somatic cell, a condition which is first clearly seen in the stage of the diaster (here only an apparent duplication in the diaster stage). As a result, there is, first, a decrease in the double number of chromosomes found in the spermatocytes of the second degree to the normal number ; second, a decrease in the number of chromosomes in the spermatocytes of the third degree (spermatids) to one-half the number present in a somatic cell, a condition probably due to the fact that here there is no stage of rest nor longitudinal splitting of the chromosomes. This is the general process in heterotypic division. Besides the heterotypic form, there occurs in the division of the spermatocytes another (homeotypic) form of karyokinetic cell-division. This differs from the heterotypic in the shortness of the chromosomes, the absence of the barrel phase, the late disappearance of the aster, and the absence of duplication in the chromosomes of the diaster. According to Meves (96), the spermatocytes of the first degree undergo heterotypic, those of the second degree, homeotypic division.
The spermatids develop into the spermatozoa, beginning immediately after the close of the second division of maturation. This process has been fully described for salamandra maculosa by Hermann, Flemming, Benda, and others, but need not engage our attention at this point beyond the statement that the chromatin of the nuclei of the spermatids develops into the heads of the spermatozoa, while the remaining structures are developed from the protoplasm. " The mature spermatozoon of the salamander represents a completely metamorphosed rell ; in the course of its development no portion of the original cell is cast off" (Meves, 97).
Spermatogenesis in mammalia may be compared to the foregoing
SPERMATOGENESIS.
375
process, with the exception that here the different stages are seen side by side in the seminiferous tubule and without any apparent sequence, making the successive stages more difficult to demonstrate. The various generations of cells form columns, and are arranged in such a manner that the younger are found near the lumen and the older close to the wall of the tubule. (Figs. 301 and
9
Fig. 301. Schematic diagram of section through convoluted seminiferous tubule
of mammal, showing the development of the spermatosomes. The number of chromosomes is not shown in the various generations of the spermatogenic cells. The progressive development of the spermatogenic elements is illustrated in the eight sectors
of the circle : a, Young sustentacular cell ; b, spermatogonium ; c, spermatocyte ; d,
spermatid. In I, 2, 3, and 4 the spermatids rest on the enlarged sustentacular cell in the
center of the sector ; on both sides of the sustentacular cells are the spermatogenic or
mother cells in mitosis. In the sectors 5, 6, 7, and 8 spermatozoa are seen in advanced stages resting on the sustentacular cells, with new generations of spermatids on
each side. [From Rauber (after Brown) with changes (after Hermann).]
302.) These columns are separated from each other by high sustentacular cells, or Sertoli's cells or columns. The metamorphosis of the cells into spermatids and spermatosomes is accomplished by the changing of the cells bordering upon the lumen and then of those in the deeper layers, etc., into spermatids and then into spermatosomes. During this process the spermatids arrange
3/6 THE GENITOURINARY ORGANS.
themselves around the ends of Sertoli's columns, a phenomenon which was formerly regarded as representing a copulation of the two elements, although it was clearly understood that no real fusion or interchange of chromatin occurred, but that the close relations of the two were for the purpose of furnishing nourishment to the developing spermatosomes. The whole forms a spermatoblast of von Ebner. Since the spermatids lining the lumen are changed into spermatozoa, and the process is repeated in the cells of the deeper layers as they come to the surface, the result is that the entire column is finally used up. The compensatory elements are supplied by the proliferation of the adjacent spermatogonia. The resulting products again divide, and thus build up an entirely new generation of spermatogenic cells. Hand in hand with these progressive phenomena occurs an extensive destruction of the cells taking part in spermatogenesis. This is shown by the presence of so-called karyolytic figures in the cells, which later suffer complete demolition.
These developmental changes are represented in the preced
Fig. 302. Section of convoluted tubule from rat's testicle (after von Ebner, 88). The pyramidal structures are the sustentacular cells, together with spermatids and spermatosomes. Between these are spermatogenic cells, some of which are in process of mitotic division. Below, on the basement membrane and concealing the spermatogonia, are black points representing fat-globules, a characteristic of the rat's testicle. Fixation with Flemming' s fluid.
ing schematic figure (Fig. 301), and may in part be observed in figure 302.
In mammalia it has been possible to trace the development of the spermatids into the spermatosomes. These phenomena have been studied and described by numerous writers, and although many conflicting views have been expressed, the essential steps of this process seem quite clearly established. The account here given is based in part on the recent observations of v. Lenhossek and the observations of Benda. Before considering the method o/ development of the spermatosomes from the spermatids, a few words concerning the structure of the latter may be useful. The sharply outlined spermatid possesses a slightly granular protoplasm and a round or slightly oval nucleus with a delicate chromatic network. In the protoplasm there is found a sharply defined globule, known as the sphere or sphere substance, which lies near the nucleus and
SPERMATOGENESIS.
377
presents throughout a nearly homogeneous structure. This substance is first noticed in the spermatocytes, disappears during the cell-divisions resulting in the spermatids, and reappears in the latter. In the protoplasm of the spermatid, lying near the nucleus, there is further found a small globular body, the chromatoid accessory nucleus of Benda, smaller than the sphere and staining very deeply in Heidenhain's hematoxylin. A true centrosome may also be found in the spermatid.
The nucleus of the spermatid develops into the head of the spermatosome, during which change the originally spheric nucleus becomes somewhat flattened and at the same time assumes a denser structure and moves toward that portion of the spermatid pointing away from the lumen of the seminiferous tubule. Accompanying these changes in the nucleus, marked changes are observed in the shape and structure of the sphere, which marks the position of the future anterior end of the head of the spermatosome, and applies itself to the nucleus on the side pointing away from the lumen of the tubule. In this position it differentiates into an outer clear homogeneous zone and a central portion which stains more deeply and to which v. Lenhossek has given the name akrosome. From these structures are developed the head-cap and the lance of the spermatosomes, which differ in shape and relative size in the spermatosomes of the different vertebrates. Recent investigation seems to establish quite clearly that the axial thread of the tail is developed from the centrosome (from the larger, if two are present), which is situated at some distance from the nucleus. Soon after the beginning of the development of the axial thread the centrosome wanders to the posterior part of the future head of the spermatosome (the pole of the nucleus opposite the head-cap) and becomes firmly attached to the nuclear membrane in this position (observations made on the rat by v. Lenhossek, and on the salamander by Meves). The middle piece and the undulating membrane, it would appear, are differentiated from the protoplasm, although the question of the mode of their development is still open to discussion. The chromatoid body assumes a position near the axial thread at its junction with the cell membrane ; its fate has not, however, been fully determined.
According to Hermann (97), the end-piece in the selachia is derived from the centrosome, the ring-shaped body from the invaginated half of the intermediate body of the spermatid formed during the last spermatocytic division, and the axial thread from filaments of the proximal half of the central spindle. The lance, according to him, represents a modified portion of the nuclear membrane of the spermatid.
For further particulars regarding spermatogenesis see the investigations of v. la Valette St. George, 67-87 ; v. Brunn, 84 ; Biondi, Benda, Meves, and v. Lenhossek.
378 THE GENITOURINARY ORGANS.
TECHNIC
The ovaries of the smaller animals are better adapted to study than those of the human being, since the former are more easily fixed.
The germinal epithelium and its relations to the egg-tubes of Pfliiger are best studied in the ovaries of young or newly born animals cats, for instance, being especially well adapted to this purpose.
Normal human ovaries are usually not easily obtainable. Human ovaries very often show pathologic changes, and in middle life frequently contain but few follicles.
Fresh ova may be easily procured from the ovaries of sheep, pig, or cow in the slaughter-houses. On their surfaces are prominent transparent areas the larger follicles. If a needle be inserted into one of these follicles and the liquor folliculi be caught upon a slide, the ovum may as a rule be found, together with its corona radiata. That part of the preparation containing the ovum should be covered with a cover-glass under the edges of which strips of cardboard are laid. If no such strips are employed, the zona pellucida of the ovum is likely to burst in the field of vision, giving rise to a funnel-shaped tear. These tears have often been pictured and described as preformed canals (micropyles).
The best fixing fluid for ovarian tissue is Flemming's or Hermann's, either of which may be used for small ovaries or pieces of large ovaries ; safranin is then used for staining. Good results are also obtained with corrosive sublimate (staining with hematoxylin according to M. Heidenhain), and also with picric acid (staining with borax carmin).
The treatment of the Fallopian tubes is the same as that of the intestine ; in order to obtain cross -sections of a tube it is advisable to dissect away the peritoneum near its line of attachment and then distend the tube before fixing. It is instructive to dilate the tube by filling it with the fixing agent, thus causing many of the folds to disappear.
No special technic is necessary in fixing the uterus and vagina. The epithelium is, however, best isolated with one-third alcohol.
Seminal fluid to which normal salt solution has been added may be examined in a fresh condition. The effect upon the spermatozoa of a very dilute solution of potassium hydrate ( i % or weaker) or of a very dilute acid (acetic acid) is worth noticing. The spermatozoa of salamandra maculosa show the different structural parts very clearly (lance, undulating membrane, marginal thread, etc.). In macerated preparations (very dilute chromic acid), or in those left for some time in a moist chamber, the fibrillar structure of the marginal and axial threads may be seen quite distinctly. The spermatozoa may also be examined in the form of dry preparations (treatment as for blood), stained, for instance, with safranin. Osmic acid, its mixtures, and osmic vapors are useful as fixing agents, certain structures being better brought out so than by employing the dry methods.
In examining the testicle (spermatogenesis) it is advisable to begin with the testis of the salamander, which does not show such complicated structures as do the testes of mammalia. Here also either Flemming's or Hermann's fluid may be used as a fixing agent, the latter being
THE SKIN. 379
followed by treatment with crude pyroligneous acid. For the salamander Hermann recommends a mixture composed of i % platinum chlorid 15 c.c. , 2% osmic acid 2 c.c., and glacial acetic acid i c.c., and for mammalia the same solution with double the amount of osmic acid. The fluid is allowed to act for some days, the specimen then being washed for twenty-four hours in running water and carried over into alcohols of ascending strengths. Paraffin sections are treated as follows : Place for from twenty-four to forty-eight hours in safranin (safranin i gm. is dissolved in 10 c.c. of absolute alcohol and diluted with 90 c.c. of anilin water). After decolorizing with pure or acidulated absolute alcohol the sections are placed for three or four hours in gentian-violet (saturated alcoholic solution of gentian -violet 5 c.c. and anilin water 100 c.c.), and are then placed for a few hours in iodo-iodid of potassium solution until they have become entirely black (iodin i, iodid of potassium 2, water 300); finally, they are washed in absolute alcohol, until they become violet with a dash of brown. The various structures appear differently stained : for instance, the chromatin of the resting nucleus and of the dispirem, bluish-violet ; the true nucleoli, red ; while, on the other hand, in the aster and diaster stages the chromatin stains red.
It is of especial importance that small testicles should not be cut into pieces before fixing, as this causes the seminal tubules to swell up and show marked changes, even in regions at some distance from the cut (Hermann, 93, I).
The treatment of the remaining parts of the male reproductive organs requires no special technic.
VI. THE SKIN AND ITS APPENDAGES.
A. THE SKIN (CUTIS).
THE skin consists of two intimately connected structures the one, of mesodermic origin, is the true skin, corium or dermis ; the other, of ectodermic origin, is the epidermis or cuticle. The superficial layer of the corium is raised into ridges and papillae which penetrate into the epidermis, the spaces between the papillae being filled with epidermal elements. Thus, the lower surface of the epidermis is alternately indented and raised into a system of furrows and elevations corresponding to the molding of the corium.
In the epidermis two layers of cells may be observed the stratum Malpighii, or stratum germinativum (Flemming), and the horny layer, or stratum corneum. According to the shape and characteristics of its cells, the stratum germinativum may also be divided into three layers first, the deep or basal layer, consisting of columnar cells resting immediately upon the corium ; second, the middle layer, consisting of polygonal cells arranged in several strata, the number of the latter varying according to the region of the body ; and third, the upper layer, or stratum granulosum, which is composed, at most, of two or three strata of gradually flattening cells characterized by their peculiar granular contents.
380
THE SKIN AND ITS APPENDAGES.
All these cell layers consist of prickle cells, and for this reason the stratum Malpighii is sometimes known as the stratum spinosum. When these cells are isolated by certain methods, their surfaces are seen to be provided with short, thread-like processes. In section the cells appear to be joined together by their processes. Since it has been proved that the processes of adjacent cells do not lie side by side, but meet and fuse, they must be regarded as belonging alike to both cells. Between the fused processes, which are known as intercellular bridges, there exists a system of channels which is in communication with the lymphatic system of the corium. The prickles just mentioned are variously regarded by different investigators ; some considering them to be exclusively protoplasmic
Fig. 303. Under surface of the epidermis, separated from the cutis by boiling. The
sweat-glands may be traced for a considerable part of their length ; X 4 : a > Sweatgland ; b, longitudinal ridge ; c, depression ; d, cross-ridge.
processes of the cells, others regarding them as derived from the membranes of the cells composing the stratum Malpighii. Ranvier and others ascribe a fibrillar structure to the peripheral portion of the cellular protoplasm, and, according to them, these fibrillae, surrounded by a small quantity of indifferent protoplasm, form the processes. Ranvier has also shown that such fibrillae may extend from one cell around several others before reaching their ultimate destination in other cells at some distance. (Fig. 305.) The cells of the stratum granulosum contain peculiar deposits of a substance to which Waldeyer has given the name of keratohyalin. This substance occurs in the form of irregular bodies varying in size and imbedded in the protoplasm. The nuclei of such cells always
THE SKIN.
381
show degenerative processes, which are possibly due to the formation of the keratohyalin (Mertsching, Tettenhamer). These karyolytic figures and keratohyalin possess in common many apparently identical microchemic peculiarities, and it is very probable that karyolysis and the formation of keratohyalin are processes originally very closely allied i. e., that the keratohyalin is derived from the fragments of the dying nucleus.
The stratum corneum forms the outer layer of the epidermis and presents, as a rule, a somewhat differentiated lower stratum. This
| Stratu .jJ
m corneum.
Stratum Malpighii.
Duct of sweatgland.
Corium.
Subcutis. ,
~~ Blood-vessel.
- -Sweat-gland.
Fig- 34- Cross-section of skin of child, with blood-vessels injected ; X 3 latter is more especially noticeable in those regions in which the stratum corneum is highly developed, and is known as the stratum lucidiim. It is quite transparent, this property being due to the presence in its cells of a homogeneous substance, which is in all probability a derivative of the more solid keratohyalin of the stratum granulosum. The cells of the stratum corneum are more or less flattened and cornified, especially at their periphery. This applies more particularly to the superficial cells. In the interior of each cell a more or less degenerated nucleus may be seen, but otherwise its contents are homogeneous, or, at most, arranged
THE SKIN AND ITS APPENDAGES.
in concentric lamellae (Kolliker, 89). Here and there between the cornified cells structures may be seen which probably represent the remains of intercellular bridges. The thickness of the epidermis varies greatly according to the locality, and is directly proportionate to the number of its cell layers. As a rule, the stratum Malpighii is thicker than the stratum corneum, but in the palm of the hand and the sole of the foot the latter is considerably the thicker.
The various layers of the epidermis are in close genetic relationship to one another. The constant loss to which the epidermis is subjected by desquamation is compensated by a continuous upward pushing of its lower elements ; cell-proliferation occurs in the basal cells and adjacent cellular strata of the stratum germinativum (Malpighii), where the elements are often seen in process of mitotic division. The young cells are gradually pushed outward, and during their course assume the general characteristics of the elements
composing the layers through which theypass. For instance, such a cell changes first into a cell of the stratum germinativum ; then, when it commences the formation of keratohyalin, into a cell of the stratum granulosum ; later, into a cell of the stratum lucidum, and finally into an element of the stratum corneum, where it loses its nucleus, cornifies, and at last drops off. The mesodermic portion of the skin, the corium, consists of a loose,
subcutaneous connective tissue containing fat, the subcutaneous layer, with the panniculus adiposus, and of the true skin, or corium proper. The amount of adipose tissue in the subcutaneous layer is subject to great variation ; there are, however, a few regions in which there is normally very little or no fat (external ear, eyelids, scrotum, etc.). To the subcutaneous connective tissue is due the mobility of the skin. The corium may be compared to the mucosa of a mucous membrane, and consists of two layers of a deeper and looser pars reticularis, and of a superficial pars papillaris supporting the papillae. The transition from the one to the other is very gradual. Elastic fibers are present in the connective tissue of both layers.
The pars reticularis is made of bundles of connective-tissue fibers arranged in a network, nearly all of the strands of which have a direo
Fibrils which pass from one __ cell to another.
Nucleolus. -
Intercellular
bridges.
Nucleus of cell.
Fig. 305. Prickle cells from the stratum Malpighii
of man ; X 4^
THE SKIN.
tion parallel with the surface of the skin and are surrounded by a reticulum of rather coarse elastic fibers. In that portion of the pars papillaris bordering upon the epidermis, the interlacing strands of connective tissue, as well as the surrounding reticulum of elastic fibers, are finer, so that the whole tissue is denser. This stratum supports the papillae knob-like or conical elevations of still denser tissue ending in one or more points. We accordingly speak of simple or compound papillae. These structures are especially numerous and well developed in the palm of the hand and sole of the foot, where they are from 1 10 // to 220 fi long. Here they rest upon ridges of the corium, which are nearly always arranged in double rows. According to whether the papillae contain blood-vessels alone, or special nerve-endings also, they are known as vascular or tactile papillae.
Stratum corneum.
Lower border of stratum lucidum. Stratum granu losum.
Stratum Malpighii.
Fig. 306. Cross-section of human epidermis ; the deeper layers of the stratum Malpighii are not represented ; X 75
The smallest papillae are found in the mammae and scrotum from
30 fj. to 50 ft long. The surface of the pars papillaris is covered by
an extremely delicate membrane the basement membrane. According to most authors, the basal cells of the epidermis are simply
cemented to this structure. Others believe that the epithelial cells
are provided with short basilar processes which penetrate into the
basement membrane and meet here with similar structures from the
connective-tissue cells of the corium. This would give the basement membrane a fibrillar structure (Schuberg).
The subcutaneous layer contains numerous more or less vertical strands of connective tissue, containing numerous large elastictissue fibers and joining the stratum reticulare of the corium to the
THE SKIN AND ITS APPENDAGES.
superficial fascia of the body or underlying structure, whatever that may be. These strands are the retinaculce cutis, and inclose in their meshes masses of fatty tissue which form the panniculu* adiposus. The latter varies greatly in thickness in different parts of the body. The vertically arranged cords of connective tissue are accompanied by blood-vessels, nerves, and the excretory ducts of glands.
Smooth muscle-fibers are also present in the skin, and around the hair follicles are grouped into bundles. Nearly continuous layers of smooth muscle tissue are found in the subcutaneous layer of the scrotum (forming here the tunica dartos), in the perineum, in the areolae of the mammae, etc. In the face and neck striated muscle-fibers also extend outward into the corium.
Even in the white race certain regions of the epidermis always contain pigment as, for instance, the areolae and mammillae of the
Stratum
corneum.
Pigment -- cell with two processes.
Pigmented
basal cell.
Fig. 307. Cross-section of negro's skin, showing the intimate relationship of the pigment cells of the corium to the basilar cells of the epidermis. The latter are more deeply pigmented at their outer ends. The pigment granules may be traced into the outermost layers of the stratum corneum ; X 5 2 5
mammary glands, the scrotum, labia majora, around the anus, etc. In these regions the epithelial cells and the connective-tissue cells of the pars papillaris corii contain a variable number of small pigment granules. The latter occur chiefly in the basal cells of the epidermis and diminish perceptibly in the cells of the overlying layers, so that in those of the stratum corneum few, if any, are left. In negroes and other colored races the deep pigmentation is due to a similar distribution of the pigment granules in the entire epidermis ; but even here the pigmentation decreases toward the surface, although the uppermost cells of the stratum corneum always contain some pigment. The nuclei of the cells are always free from the coloring-matter. The question as to the origin of the pigment is as yet unsolved. This much is known : that in those regions where pigment is present certain branched and deeply pigmented connec
THE SKIN.
385
tive-tissue cells are found immediately beneath the epiderni's, sending out processes which may be traced outward between the cells of the stratum Malpighii (Aeby). This fact has led some authors to believe that the connective tissue is in reality the source of the pigment, and that by some unknown process the latter is taken up and conveyed to the cells of the epidermis. This theory would preclude a direct production of pigment granules in the epidermal cells. But although it can not be denied that the pigment may be derived from the connective tissue, it is hardly logical to assume a priori that epithelial cells are not capable of pigment production, since, in other regions of the body, pigment formation may be observed in cells of undoubted epithelial origin, as, for instance, in ganglion cells and in
Fig. 308. A reconstruction showing the arrangement of the blood-vessels in the
skin of the sole of the foot (Spalteholz): a, Stratum Malpighii and corium; b, boundary
between cutis and subcutis, in the region of the coiled portions of the sweat-glands ;
f, subcutis ; J, subpapillary arterial network ; e, cutaneous arterial network ; f, g, //, and
t, first, second, third, and fourth venous plexuses.
the pigment epithelium of the retina. An interesting proof that the processes of pigmented connective-tissue cells actually penetrate the epidermis is afforded by the case reported by Karg, of transplantation of a piece of skin from a white man to a negro. After some time the piece of white skin became pigmented. Reinkehas demonstrated that the pigment in certain cells is in combination with certain definite bodies. The latter have been given the botanical name of trophoplasts. If the pigment be removed, colorless trophoplasts are left. They may be tinged with certain stains. In the epidermis of the white race trophoplasts are also constantly present, although they are only slightly or not at all pigmented (Barlow). 25
3 86
THE SKIN AND ITS APPENDAGES.
Stratum corneum.
Nerve-fibers in the epidermis.
Stratum Malpighii.
The following may be said concerning the vascular system of the skin : The arteries which supply the skin with nutriment penetrate the corium and form a characteristic network in its lowest stratum. They also anastomose freely in the fascia and the subcutaneous layer. From this plexus branches pass outward to form a second or subpapillary plexus. From the latter, branches are again given off which, without further anastomoses, pass along beneath the rows of papillae and supply each separate papilla with capillary twigs. These in turn pass over into venous capillaries which unite
and form four venous plexuses, one over the other and in general parallel to the surface of the skin. The uppermost venous plexus lies beneath the papillae, each venule corresponding to a single row of papillae and anastomosing with its neighbors. The second plexus is found immediately beneath the first, the third in Papillae. the lower portion of
the corium, and the fourth at the junction of the cutis and subcutis. Near the middle of the subcutis the arteries show a circular musculature, but the veins are already thus provided in the
network between the cutis and subcutis, where they also seem to possess valves. As already stated, the subcutaneous fat is divided into lobes by transverse and longitudinal bundles of connective tissue ; a second system of bundles midway between the cutis and fascia separates the panniculus adiposus into an upper and a lower layer. The former is supplied by direct arterial branches ; the latter, by branches passing backward from the cutaneous network. Those regions which are subjected to great external pressure are supplied by a greater number of afferent vessels the caliber of which is increased. In regions where the skin is very mobile the arteries are greatly convoluted. All these vascular peculiarities are present in the newborn (Spalteholz).
The lymph-vessels of the true skin are also distributed in two layers a deep and wide-meshed plexus in the subcutis, and a
Nerve-fiber.
Fig. 309. Nerves of epidermis and papillae from ball of cat's foot ; X 75
THE SKIN. 387
superficial narrow-meshed plexus immediately beneath the papillae. Into the latter empty the lymph -vessels coming from the papillae. After treating the skin by certain methods, a fine precipitate may be noticed here and there in the papillary region of the corium, a proof that lymph clefts are present. These are regarded as the beginnings of the cutaneous lymphatic system. They may also be traced into the epithelium, where they are in direct communication with the interspinal spaces between the epithelial cells (Unna). Cells are also met with in the interspinal spaces of the epidermis ; these are migratory cells, or cells of Langerhans.
The skin owes its great sensitiveness to the numerous nerves and special nerve-endings present, not only in the epithelium, but also in the corium and subcutis. In certain regions of the skin the nerves have been traced into the epithelium. In the finger-tip, for instance, numerous nerves are seen in the epidermis, where they branch and end in telodendria with or without small terminal swellings. There is no direct communication between the terminal
Nerve-fiber.
h- Nerve-fiber. \ Nerve-fiber.
Fig. 310. Meissner' s corpuscle from man ; Fig. 311. Meissner's corpuscle from man;
x 750. x 750.
nerve filaments and the epithelial cells. (Fig. 309.) In certain peculiarly sensitive regions, as the end of the pig's snout, the nervefibers end in distinct saucer-like discs (tactile menisci) which, as a rule, clasp the lower ends of the basal Malpighian cells.
The special sensory nerve -endings are situated in the corium and subcutis. Of these, we may mention the tactile corpuscles of Meissner, the end-bulbs of Krause, the Pacinian corpuscles, Ruffini's nerve-endings, and the Golgi-Mazzoni corpuscles. All these special sensory nerve-endings with the exception of the two last mentioned have been discussed in a former chapter (p. 169). Meissner's tactile corpuscles are situated in the tactile papillae of the true skin. They are especially numerous in the hand and foot.
3 88
THE SKIN AND ITS APPENDAGES.
In the distal phalanx of the index-finger every fourth papilla is a tactile papilla, containing one or sometimes two corpuscles of Meissner. They are, however, not nearly so numerous in other parts of the hand or in the foot. These corpuscles are further found on the dorsal surface of the hand and volar surface of the forearm, in the nipple and external genitals, in the eyelids (border), and in the lips. In figures 310 and 311 are shown two Meissner's corpuscles, giving the appearance presented by these end-organs when not stained with special reference to nerve terminations. For the latter see figure 137.
The Krause's end-bulbs, both spheric and cylindric, are, as a rule, situated a short distance below the papillary layer, although they are frequently found in the papillae. They occur in man in the conjunctiva, lips, and external genitals, and in the mucous membranes previously mentioned (p. 170). See page 170 and figure 136 for their structure.
In the palm of the hand and sole of the foot, the subcutaneous connective tissue contains numerous Pacinian corpuscles. They occur also along the nerve-fibers of the joints and in the periosteum of the extremities.
Very recently Ruffini demonstrated in the human corium the existence of peculiar nerve end-organs, which consist of a connective-tissue framework supporting a rich arborization of telodendria. They occur side by side with the Pacinian corpuscles and in apparently equal numbers. These nerve terminations resemble in many respects the neurotendinous spindles (see Fig. 145), although they
present certain structural differences. Instead of intrafusal tendon fasciculi, the Ruffini end-organ is composed of white fibrous and elastic tissue. In this end-organ the medullated nerves make long and tortuous turns before becoming nonmedullated, and the terminations of these nerve-fibers occupy the whole of the cross-section.
The Golgi-Mazzoni corpuscle resembles in structure the Pacinian corpuscle, although it possesses fewer lamellae and a relatively larger core, and the nerve - fibers terminating therein are more extensively branched than in the Pacinian corpuscle. Ruffini has found these nerve-endings in the subcutaneous tissue of the fingertips.
The blood-vessels of the skin are richly supplied with the vasornotor nerves, which terminate in the nonstriated muscle of the
Terminal disc of
nerve-fibers.
Epithelial cell.
Connective-tissue capsule.
- Nerve-fiber.
.Fig. 312. Grandry's corpuscles from bill of duck ; X 5
THE HAIR. 389
vessel walls. These vasomotor nerve-fibers are neuraxes of sympathetic neurones.
In aquatic birds, and more especially in ducks, the waxy skin of the beak and the cornified portion of the tongue contain the socalled corpuscles of Herbst, which resemble the Pacinian corpuscles in general structure, but have cubical cells in the core. In the same tissues are also found the corpuscles of Grandry, 60 fj. long and 40 IJL broad. They consist of a thin connective-tissue capsule, containing two or three large cells. The nerve-fiber retains its medullary sheath for some distance within the capsule. The axis-cylinder ends in discs situated between the cells inclosed by the capsule.
B. THE HAIR.
The hair and nails are regarded as special differentiations of the skin. Hair is found distributed over almost the entire extent of the skin, varying, however, in quantity and arrangement in different regions. None whatever is present in the palm of the hand and sole of the foot. In the third fetal month small papillary elevations of the skin are seen to develop in those areas in which the hairy growth later appears. Under each of these elevations there occurs a proliferation of the cells of the Malpighian layer downward into the corium. Although the elevations soon disappear, the epithelial ingrowth continues and finally forms the hair germ. This is soon surrounded by a connective-tissue sheath from the corium, in which two layers may be distinguished. At the lower end of the hair germ the corium is pushed upward, forming a papilla which penetrates into the thickened bulb of the germ. This is called the hair papilla. In the mean time the hair germ itself is undergoing marked differentiation. An axial portion, forming later the hair and inner root-sheath, and a peripheral, constituting later the outer rootsheath, are developed. From the latter are derived also the first traces of the sebaceous glands, which in the adult state are in close relationship to the hair and empty their secretion into the space between the hair and its sheath. As soon as the various layers of the hair are complete it grows outward, breaking through the overlying layers of the epidermis.
The visible portion of the hair is called the hair shaft, and that portion below the skin is the hair root. The lower portion of the hair resting upon the papilla is known as the hair bulb, and the sheaths encircling the root and bulb are called the rootsheaths, the entire structure constituting the hair follicle.
The adult hair is covered by a thin cuticle, consisting of overlying plate-like cells, i.i ft thick, most of which possess no nuclei. Beneath the cuticle is the cortical layer, composed of several strata of long, flattened cells from 4. 5 (i to 1 1 ft broad and provided with nuclei. These are also known as the cortical fibers of the hair. Upon treatment with ammonia the fibers separate into delicate
390
THE SKIN AND ITS APPENDAGES.
fibrils, the hair fibrils (Waldeyer, 82). Scattered between and within the cells of the cortical layer are varying quantities of pigment granules. The axial region of the hair is occupied by the medullary substance, from 1 6 // to 20 // in diameter. This may be lacking ; but if present, consists of from 2 to 4 strata of polygonal, nucleated and pigmented cells. The hair shaft often contains air vesicles.
The inner root-sheatJi consists of three concentric layers first, of an outer single layer of clear nonnucleated cells, the so-called
Fig- 3 T 3- Transverse section of human scalp; X I2: A P, Musculus arrector pili ;
c, corium ; ep, epidermis; fp, hair follicle ; Gap, aponeurosis ; gls, sweat-gland ; glse, sebaceous glands; KH, club-hair; //, papilla of hair; Re, retinacula cutis; Rp, root of hair;
Sp, shaft of hair; ts, subcutaneous layer (Sobotta, "Atlas and Epitome of Histology" ).
layer of Henle ; second, of a thicker middle layer, made up of a stratum of nucleated cells containing keratohyalin, the layer of Huxley ; and, third, of an inner cuticle, bordering upon the hair.
The outer root-sheath is made up of elements from the stratum germinativum. Here we have to do with prickle cells, surrounded by an outer layer of columnar elements. The connective-tissue portion of the hair follicle is composed of an outer, looser layer of longitudinal fibrous bundles ; of an inner, compacter layer of circu
THE HAIR.
391
lar fibers ; and of an innermost well-developed basement membrane the glassy membrane.
At a certain distance above the root bulb all the layers of the
The hair.
Stratum Malpighii of outer root-sheath.
^L Hair papilla.
Inner
rootsheath.
Glassy layer of hair bulb.
Connective tis sue of the
cutis.
Fig. 314. Longitudinal section of human hair and its follicle ; X about 300.
epithelial portion of the hair follicle are well developed and distinct from each other. This condition changes toward the hair papilla
392
THE SKIN AND ITS APPENDAGES.
as well as toward the hair shaft. Below, in the region of the thickened hair bulb, the root-sheaths begin to lessen in thickness, their layers becoming more and more indistinct toward the base of the hair papilla. Finally, all differentiation is lost in the region where they encircle the neck of the papilla. Toward the shaft of the hair, the root-sheath also undergoes changes. In the region into which the sebaceous glands empty, the inner root-sheath disappears, while the outer becomes continuous with the stratum germinativum of the epidermis ; the outer layers of the latter the stratum granulosum, stratum lucidum, and stratum corneum push downward between the outer root-sheath and the hair to the openings of the sebaceous glands.
Regarding the growth of the hair, two theories are prevalent.
Glassy
layer.
_ Cortex of hair.
_ Medulla of hair.
_ Cuticle of inner rootsheath.
Henle's layer.
Fibrous-tissue sheath.
Fig. 3 T 5 Cross-section of human hair with its follicle ; X about 300.
The one theory assumes that the elements destined to form the epithelial root-sheaths are derived from the epidermis by a constant process of invagination. The component parts of the hair would thus be continuous with the layers of the root-sheaths, and consequently with those of the epidermis. Thus the basal cells of the external root-sheath would extend over the papilla, and be continuous with the cells of the medulla of the hair (these relations are especially well defined in the rabbit), and the stratum spinosum (middle layer of stratum Malpighii) of the outer root-sheath would be continuous with the cortical substance of the hair. According to this theory also, the layer of Henle would correspond to the stratum lucidum of the epidermis, and at the base of the hair
THE HAIR.
393
Nerve plexus of Bonnet.
would become its cuticle, while the layer of Huxley would form the cuticle of the inner root-sheath (Mertsching). The other theory assumes that the hair is derived from a matrix, consisting of proliferating cells situated on the surface of the papilla. From these germinal cells would be derived the medullary and cortical substance of the hair, its cuticle, and the inner root-sheath (Unna).
The shedding of hair is common to all mammalia, a phenomenon occurring periodically in the majority of species. In man the process is continuous. Microscopic examination shows that the hair destined to be shed becomes loosened from its papilla by a cornification of the cells of its bulb. At the same time the cortical portion of the hair bulb breaks up into a brush-like mass. Such hairs are called club hairs or bulb hairs, in contradistinction to papillary hairs. In the region of the former papilla there arises, by a proliferation of the external root-sheath, a bud which grows downward, from which a new hair with its sheaths and connective-tissue papilla is developed. The result is that the developing new hair gradually pushes the old hair outward until the latter finally drops out. The exact details of this process have given rise to considerable discussion (yid. Gotte and Stieda, 87).
Adjacent to the hair follicles are bundles of smooth musclefibers, known as the arrectores pilorum. They originate from the papillary layer of the corium and extend to the lower part of the connective-tissue sheath of the hair follicles. In their course they not infrequently encircle the sebaceous glands of the follicle. Since
the hair follicles have a direction oblique to the skin surface, forming with it an acute and an obtuse angle, and since the muscle is situated within the obtuse angle, its function may easily be conceived as being that of an erector of the hair. The hair papillae are very vascular.
The nerve-fibers of the hair follicles have recently been studied by a number of investigators, with both the Golgi and the methyleneblue methods. It has been shown that the hair follicles receive their nerve supply from the nerve-fibers which terminate in the immediate skin area. Each follicle receives, as a rule, only one nerve-fiber, which reaches the follicle a short distance below the mouth of the sebaceous gland. The nerve-fiber, on reaching the
Fig. 316 Longitudinal section
through hair and hair follicle of cat ;
X 1 60.
394 THE SKIN AND ITS APPENDAGES.
follicle, loses its medullary sheath and divides into two branches, which surround it in the form of a ring. From this complete or partial ring of nerve-fibers numerous varicose fibers proceed upward parallel to the axis of the follicle for a distance about equal to the cross-diameter of the follicle, to terminate, it would seem, largely outside of the glassy layer (Retzius). In certain mammalia the nerve-fibers end in tactile discs, found in the external root-sheaths of the so-called tactile hairs. The muscles of the hairs receive their innervation through the neuraxes of sympathetic neurones, which reach the periphery from the chain ganglia through the gray rami communicantes. These nerves are known as pilomotor nerves, and when stimulated, excite contraction of the erector muscles of the hairs, causing these to assume an upright position and producing the appearance termed goose skin, or cutis anserina. Langley and Sherrington have made interesting and important observations on the course and distribution of the pilomotor nerves.
C. THE NAILS.
The nails are a peculiar modification of the epidermis. The external arched portion is called the body of the nail ; that area upon
Nail wall.--- _^ Nail.-M
^'"-,
Stratum -i : . Malpighii. ; Stratum cor--"""" 1 -" neum of the nail groove. <
-Bloodvessel.
Fig. 3'7- Longitudinal section through human nail and its nail groove (sulcus) ; X 34 which the latter rests, the nail bed, or matrix ; and the two folds of epidermis which overlap the nail, the nail walls. The groove which exists between the nail wall and nail bed is known as the sulcus of the matrix, and the proximal imbedded portion of the nail as the nail root, since all growth of the nail takes place in this region. The nail bed consists of the corium, which is here made up of a dense felt-work of coarse connective-tissue fibers. Immediately beneath the nail the corium is raised into a number of more or less symmetric longitudinal ridges, which again become continuous with the connective-tissue papillae of the skin at the line where the nail projects beyond its bed.
The depressions between the ridges are occupied by epidermal cells, which also form a thin covering over the ridges themselves.
THE NAILS. 395
These cells correspond here to the basilar layer of the stratum Malpighii. The stratum granulosum is not uniformly present, although occurring as isolated areas in the region of the nail root and lunula, the white area of demilunar shape at the proximal portion of the nail. Unna has demonstrated that the pale color of the lunula and root of the nail is due to the presence of keratohyalin. Formerly, this peculiarity was attributed to a difference in the distribution of the vessels in the various portions of the nail bed. The body of the nail, with the exception of the lunula, is transparent a condition which may be explained by the fact that the elements of the nail correspond to those of the stratum lucidum. As a consequence, the vessels of the matrix shine through, except at the lunula, where the keratohyalin granules render the nail opaque.
The nail itself consists of elements homologous to those of the stratum lucidum. They are flat, transparent cells, closely approximated, and all contain nuclei. The cells overlie each other like tiles, and are so arranged that each succeeding lower layer projects
Corium.
. J Blood-vessel .
Fig. 318. Transverse section through human r.ail and its sulcus ; X 34 a little further distalward than the preceding. At the period when the nails are formed, about the fourth month of fetal life, sulci are already present. The first trace of the nail is seen as a marked thickening of the stratum lucidum in the region which later becomes the body of the nail ; in this stage the structure is still covered by the remaining layers of the stratum corneum, constituting the eponychium. The embryonal nail then spreads in all directions until it finally reaches the sulcus. Henceforward the growth is uniform. The eleidin normally present in the stratum lucidum of the skin also occurs in the nail, and is derived, as we have already seen, from the keratohyalin. It may readily be conceived that later, when growth is confined to the root of the nail, keratohyalin is also present. As soon as the nail begins to grow forward, in the ninth month, the greater, part of the eponychium is thrown off; but during the entire extrauterine life, a portion of the eponychium is retained at the nail wall, and as hyponychium on the anterior and under surface of the nail.
396
THE SKIN AND ITS APPENDAGES.
D. THE GLANDS OF THE SKIN.
The glands in the skin are of two kinds sweat-glands and sebaceous glands. In this connection we may also consider the mammary glands, which may be regarded as a modified skin gland.
I. The Sweat-glands. The sweat-glands, or sudoriparous
Fig. 319. A, B, Two views of a model of the coiled portion of a sweat-gland from the plantar region of a man, reconstructed by .Bern's wax-plate method ; X Io ( Huber-Adamson).
glands, are distributed throughout the entire skin, but are especially numerous in certain regions as, for instance, the axilla, palm of the hand, and sole of the foot. They lie imbedded either in the adipose tissue of the true skin, or still deeper in the subcutaneous connective tissue.
The sweat-glands are simple tubular in type, and their secreting
portion is coiled ; hence the name coil-glands. The coiled portion of these glands measures 0.3 to 0.4 mm. The excretory duct is nearly straight in its course through the corium. From here on its course is spiral, and it should be borne in mind that in its passage through the epidermis it has no other wall than the epidermal cells of the various layers through which it passes, although these cells are arranged concentrically around the lumen of the duct. The duct takes part in the formation of the coiled portion of the gland, forming about onefourth of the length of the tubule which takes part in the formation
Basement
membrane.
Nonstriated muscle-cell.
Gland-cell.
Fig. 320. Cross - section of tubule of coiled portion of sweat-gland of human axilla. Fixation with sublimate ; X 600.
THE GLANDS OF THE SKIN.
397
Nucleus of nonstriated muscle-cell.
Nucleus of gland-cell.
of the coil. In figure 319 are shown two views of a model of the coiled portion of a sweat-gland from the plantar region of the foot of a man. The length of the tubule in the coiled portion of this gland measures 4.25 mm., of which 1.25 mm. fall to the excretory duct and 3.0 mm. to the secretory tubule.
The blind end of the secreting portion of the tubule and the excretory duct as it enters the coil are usually in close proximity. The secretory portion of the tubule of sweat-glands is lined by a single layer of cubic or columnar cells, with finely granular protoplasm and round or oval nuclei possessing one or two nucleoli. Between this layer of cells and the basement membrane there is found a layer of nonstriated muscle-cells, longitudinally disposed. The portion of the excretory duct found within the coil of the glands is lined by a single layer of short cubic cells, with cuticular border, outside of which there is a delicate basement membrane. The muscular layer is lacking in this and the remaining portion of the duct The excretory portion of the duct passing through the corium is lined by short, somewhat irregularly cubic cells arranged in two layers.
Capillary networks surround the secreting portions of the sweat-glands.
The nerves of the sweatglands have been studied with the aid of the methylene-blue method by Ostroumow, working under Arnstein's direction. These glands receive their innervation through the neuraxes of sympathetic neurones,
the terminal branches of which form an intricate network just outside of the basement membrane, known as the epilamellar plexus, From this plexus fine varicose nerve-fibers pass through the basement membrane, and, after coursing a shorter or longer distance with or without further division, end on the gland-cells, often in clusters of small terminal granules united by delicate threads.
The development of the sweat-glands begins in the fifth month of fetal life. At first solid cords grow from the stratum germinativum of the epidermis into the corium. Later, in the seventh month, these become hollow.
Joseph has shown a structural change in the secretory cells 01" the sweat-glands when perspiration was induced by electrical stimulation or by drugs.
With the sweat-glands as here described, and which have, as
Fig. 321. Tangential section through
coiled portion of sweat-gland from human
axilla. Sublimate fixation ; X 7
398 THE SKIN AND ITS APPENDAGES.
has been stated, a very wide distribution, we may also class certain skin glands, grouped under the term of "modified sweat-glands," which show certain structural and morphologic peculiarities and are found in special regions of the body. To these belong the axillary glands, the circumanal glands, the ciliary glands or glands of Moll of the eyelid, and the ceruminous glands of the external auditory canal. The axillary glands resemble the sweat-glands in shape and structure, possessing, however, larger and longer tubules. The coiled portions of these glands measure 1.5 to 2 mm., the tubule of the coil attaining a length of 30 mm. In the circumanal region are found several types of sweat-glands, especially in an area having the form of an elliptical ring with a width of about 1.5 cm. and situated about 1.5 cm. from the anus. In this region there
Fig. 322. Model of a sebaceous gland with a portion of the hair follicle, reconstructed
by Born's wax-plate method. A, Hair follicle.
are found large sweat-glands, known as the circumanal glands of Gay ; branched sweat-glands of the type of tubulo-alveolar glands ; sweat-glands with relatively straight ducts, ending in a relatively' large saccule or vesicle, from which arise secondary tubules or alveoli ; and, finally, sweat-glands of the type as found in other regions of the body. The ciliary glands or glands of Moll may also be classed as branched glands of the type of tubulo -alveolar glands, with relatively large vesicles. The ceruminous glands are branched tubulo-alveolar glands.
2. The Sebaceous Glands. The distribution of the sebaceous glands in the skin is closely connected with that of the hair follicles into which they pour their contents. Exceptions to this rule occur
THE GLANDS OF THE SKIN.
399
in only a few regions of the body, as, for instance, in the glans penis and foreskin (Tyson's glands), in the labia minora, angle of the mouth, glandule tarsales, and the Meibomian glands of the eyelids, etc. As a rule the sebaceous gland empties by a wide excretory duct into the upper third of the hair follicle. The walls of the duct also produce secretion, and can therefore hardly be differentiated from the rest of the gland. At its base the duct widens and is provided with a number of simple or branched alveoli. The sebaceous glands are therefore of the type of simple branched alveolar glands, varying in length from 0.2 mm. to 0.5 mm. They are surrounded by connective-tissue sheaths, which at the same time cover the hair follicles. Inside of the sheath is the membrana propria, which is a continuation of the glassy membrane of the follicle. The two or three basal strata of glandular cells must be regarded as a direct continuation of the elements of the external root-sheath. In the
Fig. 323. Section of alveoli from sebaceous gland of human scalp.
more centrally placed strata the cells are distinctly changed in character ; their contents consist of fat globules, varying in size and distributed throughout the protoplasm, giving this a reticular appearance, while the nuclei suffer compression from the accumulation of the fat globules and gradually become smaller and more angular. Finally, the cells change directly into secretion, which is then poured into the hair follicle as sebum. It is thus seen that in the secretion of sebum the cells are consumed and must be replaced. This renewal takes place by the constant proliferation of the basilar cells, which push the remains of the secreting cells upward and finally take their places. The final disintegration of the cells occurs either within the gland itself or between the hair follicle
4OO THE SKIN AND ITS APPENDAGES.
and the hair. The secretion contains fatty globules of varying size, which occur either free or attached to cellular detritus.
3. The Mammary Glands. The mammary glands are also included among the cutaneous glandular structures. They are developed early, but not until the fifth month is it possible to distinguish a solid central portion, with radially arranged tubules terminating in dilatations. The structures are all derived from the basal layers of the epidermis. From birth to the age of puberry
Fig. 324. Model of a small portion of a secreting mammary gland ; X 2O (Maziarski, Anatomische Hefte, vol. xvm.J
the organs are in a state of constant growth, and are early surrounded by a connective-tissue sheath. The alveoli, which have been developed in the mean time, are still solid and relatively small. Up to the twelfth year the glands remain identical in structure in boys and girls. In the female the mammary glands continue to develop from the age of puberty ; in the male, on the other hand, they undergo a retrograde metamorphosis, ending, finally, in the atrophy of all except the excretory ducts. The mammary glands do not attain their full stage of development in women until the last months of pregnancy, and are functionally active at parturition. The human mammary gland when fully developed has the following structure : It consists of about twenty lobes, separated from each other by connective-tissue septa. These lobes are again divided into a larger number of lobules, and these in turn are composed of numerous irregularly round or oval or even tubular alveoli. The alveoli are provided with small excretory passages, which unite to form the smaller ducts, these in turn uniting to form the larger ducts. Shortly before terminating at the surface of the mammilla, each mammary duct widens into a vesicle, the sinus lactiferus. The number of excretory ducts corresponds to that of the larger lobes. The ducts are lined by simple cubical epithe
THE GLANDS OF THE SKIN.
4OI
Hum, except near their termination in the nipple, where they are lined by stratified pavement epithelium, and surrounded by a fibrous tissue sheath.
The epithelium of the alveoli differs according to the state of functional activity. In a state of rest it consists of a single layer of glandular cells of nearly cubical shape which stain deeply, the internal surfaces now and then projecting slightly into the lumen. At the beginning of secretion fat globules make their appearance in the distal ends of the cells. At the same time a corresponding
Alveolus.
Connectivetissue stroma.
)uct and alveoli.
Adipose tissue.
Fig. 325. From section of mammary gland of nullipara. (From Nagel's "Die weiblichen Geschlechtsorgane," in " Handbuch der Anatomic des Menschen," 1896.)
increase in size occurs throughout the entire alveolus. There are as yet current two quite contradictory views as to the manner in which the milk is secreted. According to certain observers, the free ends of the cells, which contain the most fat globules, are constricted off, after which the fat globules are freed in the lumen. The secretory portion of the alveolus is then composed of low epithelial cells, in which the process begins anew. The process of milk secretion therefore consists in throwing off the inner halves of the cells containing the fat globules, and in regeneration of the cells from the 26
4O2 THE SKIN AND ITS APPENDAGES.
nucleated remains of the glandular epithelium. Whether a karyokinetic division of the nuclei occurs in this process is not known, and how often the process of regeneration may be repeated in a single cell is not capable of demonstration. It is -certain, however, that entire cells are destroyed, to be replaced later by new elements. Other observers regard the secretion of milk as occurring without a partial or total destruction of the secretory cells, but after the manner of the secretion of other glands. This latter view seems more in accord with the more recent observations. The membrana propria of the alveoli appears homogeneous. Between it and the glandular cells are so-called basket cells, similar to those in the salivary glands. Benda regards the basket cells as nonstriated muscle elements having a longitudinal direction, making the structure of the alveoli of the mammary gland similar in this respect to that of the secreting portion of the sweat-glands.
The skin of the mammilla is pigmented, and the papillae of its corium are very narrow and long. In the corium are also found large numbers of smooth muscle-fibers, which form circular bundles around the excretory ducts. In the areolse of the mammae are the so-called glands of Montgomery, which very probably represent accessory mammary glands. These are especially noticeable during lactation. The blood-vessels of the mammary gland, the larger branches of which are situated mainly in the subcutaneous tissue, form rich capillary networks about the alveoli.
The mammary glands possess many lymphatics. These are especially numerous in the connective-tissue stroma between the lobules. The lymph-vessels collect to form two or three larger vessels, which empty into the axillary glands. The mammary gland receives its nerve supply from the sympathetic and cerebrospinal nervous systems through the fourth, fifth, and sixth intercostal nerves. The terminations of the nerves in the mammary gland have been studied by means of the methylene-blue method by Dmitrewsky, working in the Arnstein laboratory, who finds that the terminal branches form epilamellar plexuses outside of the basement membrane of the alveoli, from which fine nerve branches pass through the basement membrane and end on the gland cells in clusters of terminal granules united by fine filaments. The nipple has a rich sensory nerve supply. In the connective-tissue papillae are found tactile corpuscles of Meissner.
The milk consists of fat globules of varying size, which, however, do not coalesce an attribute due to the presence of albuminous haptogenic membranes surrounding the globules. Shortly before, and for some days after, parturition the milk contains true nucleated cells in which are fat globules ; these are known as the colostrum corpuscles. They probably represent leucocytes which have migrated into the lumen of the gland and have taken up the fat globules of the milk. This milk is known as colostrum.
TECHNIC. 403
TECHNIC.
Good general views of the skin can be obtained only from sections. Any fixation method may be employed, although alcohol is preferable on account of the better subsequent staining. For detail work Flamming' s solution, corrosive sublimate, or osmic acid is the best. Sectioning of the skin is attended with many difficulties, and large pieces can be cut only in celloidin. Small and medium-sized pieces may be cut in paraffin ; but even in this case the skin must be rapidly imbedded in the paraffin /'. e., it must not remain too long in either alcohol or toluol and the paraffin must have only the consistency necessary to cut well (about 50 C. meltingpoint). In order to obtain good paraffin sections of the skin the following procedure is recommended : Pieces fixed in Flemming's solution or osmic acid are kept in 96% alcohol, then placed for not more than twentyfour hours in absolute alcohol and imbedded in paraffin by means of the chloroform method. In the chloroform, chloroform -paraffin, and pure paraffin they remain for one hour each. The paraffin used should consist of two parts paraffin of 42 C. , and one part paraffin of 50 C. melting-point. The thermostat must be kept at 50 C. (R. Barlow). The sections should not be mounted by the water-albumen method.
In sections of epidermis which have been freshly fixed with osmic acid, the stratum corneum may be clearly differentiated into three layers (probably because of the defective penetration of the reagent) into a blackened superficial, a middle transparent, and a still lower black layer (vid. Fig. 326).
In tissue fixed in alcohol or corrosive sublimate the stratum lucidum stains yellow with picrocarmin, but is very weakly colored by basic anilin stains. In unstained preparations the stratum lucidum is glass-like and transparent. Eleidin is diffusely scattered throughout both the stratum lucidum and stratum corneum. Like keratohyalin, it stains with osmic acid and also with picrocarmin, but not with hematoxylin. Nigrosin stains eleidin, but not keratohyalin.
Keratohyalin is insoluble in boiling water and is not attacked by weak organic acids. It dissolves, however, in boiling acetic acid, but is not changed by the action of pepsin or trypsin. The keratohyalin granules of the stratum granulosum swell in from i c / f to 5 c /o potassiumhydrate solution ; under the influence of heat these granules together with the cells containing them are finally dissolved. They are not attacked by ammonia, and remain unaffected for a long time in strong acetic acid. As ammonia and acetic acid render the remaining portions of the tissue transparent, these reagents may be employed for the rapid identification of keratohyalin. The larger flakes of keratohyalin swell in sodium carbonate solution (i%), but not the smaller granules, and it would seem that the larger granules have less power of resistance than the smaller. Keratohyalin remains unchanged in alcohol, chloroform, and ether, but is digested in trypsin and pepsin (not, however, the keratin). Keratohyalin can be stained with hematoxylin and most of the basic anilin dyes.
The prickles of the cells composing the stratum Malpighii may be seen in very thin sections (not over 3 // in thickness) of skin previously fixed in osmic acid. In this case it is best to employ not Canada balsam, but glycerin, which does not have so strong a clearing action. Isolation of the prickle cells is best accomplished as follows (Schieffer
404
THE SKIN AND ITS APPENDAGES.
decker): A fresh piece of epidermis is macerated for a few hours in filtered, cold-saturated, aqueous solution of dry pancreatin ; the whole may then be preserved for any length of time in equal parts of glycerin,
Outer dark layer.
Stratum corneum. Middle light layer.
Inner dark layer. Stratum lucidum.
Stratum Malpighii.
Cut is and subcutis.
Fat cell.
Fig. 326. Transverse section through the human skin. Treated with osmic acid ; X 30 : a, Part of the tortuous duct of a sweat-gland in the epidermis ; b, duct of same sweat-gland in the corium.
water, and alcohol. Small pieces taken from such specimens are readily teased and show both isolated and small groups of attached prickle cells.
The distribution of the pigment in the skin is best studied in unstained sections. With a nearly closed diaphragm and under medium magnification the pigment granules appear darker on raising the tube and lighter upon lowering it.
In sections of skin treated with Flemming's fluid, the structure of the cutis also may be studied. The medullary sheaths of the nervefibers and the fat appear black. In preparations stained with safranin the elastic fibers are colored red and are very distinct (Stohr and O. Schultze). For the orcein method according to Unna, see p. 128.
Hair may be examined in water without further manipulation. The cuticle is then seen to consist of polygonal areas, the border-lines of which correspond to the limits of the flattened cells. By slightly lowering the objective the cortical substance comes into view with its indistinct
TECHNIC. 405
striation and occasional pigmentation. The medullary substance, if present, may also be seen with its vesicles containing air. Both the cortical and cuticular cells may be isolated, the process consisting in treating the hairs for several days with 33 c / c potassium hydrate solution at room temperature, or in heating the whole for a few minutes. Concentrated or weak sulphuric acid produces the same result. On warming a hair in sulphuric acid until it begins to curl and then examining it in water, we find that the cortical and medullary layers as well as the cuticle are separated into their elements. Treatment of the skin with Miiller's fluid, alcohol, or sublimate is recommended for the examination of hair and hair follicles. The orientation of the specimen should be very precise, in order to obtain exact longitudinal or cross-sections of the hair. There is hardly a structure of the body which is more suitable for staining with the numerous coal-tar colors than the hair and its follicle (Merkel).
The corpuscles of Meissner may be best obtained from the end of the finger. After boiling a piece of fresh skin from the finger-tip for about a quarter of an hour, the epidermis may be easily removed ; the papillae are now seen on the free surface of the cuds. A portion of the latter is cut away with a razor and examined in a 3 % solution of acetic acid. The corpuscles are readily distinguished. Their relations to the nerves should be studied in specimens fixed with osmic acid or gold chlorid. The terminations of the nerves in these end-organs are best seen in preparations stained after the infra vitam methylene-blue method.
The corpuscles of Herbst and Grandry are found in the waxy skin covering the bill, and in the palate of the duck (especially numerous in the tongue of the woodpecker). For the study of the nervous elements the following method is useful : Pieces of the waxy skin are removed with a razor and placed for twenty minutes in 50% formic acid. After washing the specimens for a short time in distilled water they are transferred to a small quantity of i c /c gold chlorid solution (twenty minutes), then again rinsed in distilled water, and placed for from twentyfour to thirty-six hours in the dark in a large quantity (^ liter) of Pichard's solution (amyl alcohol i part, formic acid i part, water 100 parts). After again washing in water the specimens are transferred to alcohols of gradually increasing strengths and finally imbedded in celloidin or celloidin-paraffin.
The Pacinian corpuscles occur in the mesentery of the cat and may be examined in physiologic saline solution.
The nerves of the epidermis are demonstrated by the goldchlorid method (see p. 48). But even here the chrome-silver method and the intra vitam methylene-blue method yield extremely good results, and may be used with great advantage in the study of the nerves in the cutis.
The so-called tactile menisci are very numerous in the snout of the pig and the mole. Bonnet recommends for these structures fixation in -33% chromic acid solution, overstaining with hematoxylin, and differentiation in an alcoholic solution of potassium ferricyanid.
406 THE CENTRAL NERVOUS SYSTEM.
VII. THE CENTRAL NERVOUS SYSTEM.
IN a study of the minute anatomy of the central nervous system consideration should be given to the arrangement of the nerve-cells and nerve-fibers in the various regions, and to the mutual relations which the elements of the nervous system bear to one another. In a text-book of this scope, however, we shall be unable to enter into the consideration of these subjects in detail, but must content ourselves with a very general discussion of the structure of certain regions of the central nervous system and an account of a few typical examples illustrating the mutual relationship of the nerve-elements to one another. We shall, therefore, give a general description of the structure of the spinal cord, cerebellum, cerebrum, olfactory lobes, and ganglia. In this description we have drawn freely from the results of the researches of Golgi (94), Ramon y Cajal (93 l )> von Lenhossek (95), Kolliker (93), and van Gehuchten (96). '
A. THE SPINAL CORD.
The spinal cord extends from the upper border of the atlas to about the lower border of the first lumbar vertebra. It has the form of a cylindric column, which at its lower end becomes quite abruptly smaller, to form the conns medullaris, and terminates in an attenuated portion the filum terminate. It presents two fusiform enlargements, known as the cervical and lumbar enlargements respectively. The spinal cord is partly divided into two symmetric halves by an anterior median fissure and by a septum of connective tissue, extending into the substance of the cord from the pia mater (one of the fibrous tissue membranes surrounding the cord), and known as the posterior median septitm. Structurally considered, the spinal cord consists of white matter (mainly medullated nerve-fibers) and gray matter (mainly nerve-cells and medullated nerve-fibers). The white and the gray matter present essentially the same general features at all levels of the spinal cord, although the relative proportion of the two substances varies somewhat at different levels. The different portions of the cord present also certain structural peculiarities.
The distribution of the gray and the white substances of the spinal cord is best seen in transverse sections.
The varying shape of the spinal cord in the several regions and the changing relations of the gray to the white substance are shown in the illustrations of cross-sections of the adult human spinal cord (see p. 407).
The gray substance is arranged in the form of two crescents, one in each half of the cord, united by a median portion extending from one half of the cord to the other, the whole presenting somewhat the form of an H. The horizontal part contains the commis
THE SPINAL CORD.
407
Fig. 327. Four cross-sections of the human spinal cord ; X 7 : ^ Cervical region in the plane of the sixth spinal nerve-root ; J3, lumbar region ; C, thoracic region ; Z>, sacral region (compare with Fig. 328). (From preparations of H. Schmaus.)
408 THE CENTRAL NERVOUS SYSTEM.
sures and the central canal of the spinal cord, while the vertical limbs or crescents extend to the ventral and dorsal nerve-roots, forming the anterior and posterior horns. The former are, as a rule, the larger, and at their sides (laterally) the so-called lateral horns may be seen, varying in size in different regions. In each anterior horn are three main groups of ganglion cells : the ventrolateral, made up of root or motor nerve-cells ; the ventromesial, composed of commissural cells ; and the lateral (in the lateral horn), containing column cells. At the median side of the base of each posterior horn we find a group of cells and fibers known as the column of Clark, most clearly defined in the dorsal region, while in the posterior horn itself is the gelatinous substance of Rolando. Aside from these, numerous cells and fibers are scattered throughout the entire gray substance.
The motor nerve-cells lie in the ventrolateral portion of the anterior horn, their neuraxes extending into the anterior nerve-root. Their dendrites are distributed in a lateral, dorsal, and mesial direction, the two former groups ending in the anterior and lateral columns, the mesial in the region of the anterior commissure. Some of the mesial dendrites extend beyond the median line and form a sort of commissure with the corresponding processes of the other side. The commissural cells lie principally in the mesial group of the anterior horn, but occur here and there in other portions of the gray substance. Their neuraxes form the anterior gray commissure with the corresponding processes from the other side. After entering the white substance of the other side, these neuraxes undergo a T-shaped division, one branch passing upward and the other downward. The column cells are small multipolar elements, represented by the cells of the lateral horns, although they are also found throughout the entire gray mass. Their neuraxes pass directly into the anterior, lateral ^ and posterior horns.
The cells of the column of Clark, or micleus dorsalis, are of two kinds those in which the neuraxes pass to the anterior commissure (commissural cells) and those in which the neuraxes pass into the direct cerebellar tract of the same side. The plurifunicular cells are cells the neuraxes of which divide two or three times in the gray substance, the branches then passing to different columns of the white matter on the same or opposite side of the cord. In the latter case the branches must necessarily extend through the commissure. The cells of the substantia gclatinosa (Rolando) are cells with short, freely branching neuraxes, which end after a short course in the gray mass (Golgi's cells). The posterior horn contains marginal cells, spindle-shaped cells, and stellate cells. The first are situated superficially near the extremity of the posterior horn, their neuraxes extending for some distance through the gelatinous substance of Rolando and then into the lateral column. The spindle-shaped cells are the smallest in the spinal cord and possess a rich arborization of dendrites extending to the nerve-root of the pos
THE SPINAL CORD.
409
terior horn. Their neuraxes, which originate either from the cellbody or from a dendrite, pass over into the posterior column. The stellate cells are supplied with dendrites, which either branch in the substance of Rolando or extend into the column of Burdach.
The gray matter contains, further, numerous medullated nervefibers, in part the neuraxes of the nerve-cells previously mentioned, and in part collateral and terminal branches of the nerve-fibers of the white matter with their telodendria ; also supporting cells, known as neurogliar cells (to be discussed later), and blood-vessels.
The white matter of the spinal cord consists of medullated fibers, which are devoid of a neurilemma, of neurogliar tissue, and of fibrous connective tissue.
In each half of the cord the white substance, which surrounds the gray, is separated by the gray matter and its nerve-roots into
Posterior horn cell.
Crossed pyramidal column.
Golgi cell of posterior horn.
Direct cerebellar column. Column cells.
Golgi'scommissural cells.
Gowers'
column. Motor cells.
Collaterals
of crossed
pyramidal
column.
Collaterals ending in the gray matter.
Direct pyramidal column.
Fig. 328. Schematic diagram of the spinal cord in cross-section after von Lenhossek, showing in the left half the cells of the gray matter, in the right half the collateral branches ending in the gray matter.
three main divisions or columns: The first division, lying between the anterior median fissure and the anterior horn, is the anterior column ; the second, lying between the anterior and posterior horns, is the lateral column (since the anterior and lateral columns belong genetically to each other, the term anterolateral column is often used) ; and the third, lying between the posterior nerve-root and the posterior median septum, is the posterior column.
By means of certain methods it has been possible to separate the white substance into still smaller divisions, the most important of which may here be described.
In each anterior column is found a narrow median zone extending along the entire length of the anterior median fissure and con
4io
THE CENTRAL NERVOUS SYSTEM.
THE SPINAL CORD. 411
taining nerve-fibers which come from the pyramids of the medulla. The majority of the pyramidal fibers cross from one side of the cord to the other in the lower portion of the medulla, at the crossing of the pyramids, and form a large bundle of nerve-fibers found in each lateral column, which will receive attention later. Some of the pyramidal fibers descend into the cord on the same side, to cross to the opposite side at different levels in the cord. These latter fibers constitute the narrow median zone, on each side of the anterior median fissure previously mentioned, forming the anterior or direct pyramidal tract, or the column of Tiirck. Between the direct pyramidal tract and the anterior horn lies the anterior ground bundle.
In the lateral columns are found a number of secondary columns, which may now be mentioned. In front of and by the side of the posterior horn in each lateral column lies a large group of nerve-fibers, forming a bundle which varies somewhat in size and shape in the several regions of the spinal cord, but which has in general an irregularly oval outline. These nerve-fibers are the pyramidal fibers, previously mentioned, which in the lower part of the medulla cross from one side to the other, and for this reason are known as the crossed pyramidal fibers, forming the crossed pyramidal columns. External to these columns and to the posterior horns, and extending from the posterior horns half-way around the periphery of the lateral columns, lie the direct cerebellar columns, consisting of the neuraxes of the cells of the columns of Clark, which have an ascending course. Lying just external to and between the anterior and posterior horns is a somewhat irregular zone, the mixed lateral column, containing several short bundles of fibers, the anterior of which are probably motor ; the posterior, sensory. In the ventrolateral portions of the lateral columns, between the mixed lateral and the direct cerebellar columns and extending as far backward as the crossed pyramidal columns, lie two not well-defined columns, known as the ascending anterolateral or Gowers's columns and the descending anterolateral columns ; the former are nearer the outer portion of the cord.
In the posterior column we distinguish a median and a lateral column. The former lies along the posterior median septum, and may even be distinguished externally by an indentation ; its upper portion tapers into the fasciculus gracilis. This is the column of Goll, and it contains ascending or centripetal fibers. The lateral tract lies between the column of Goll and the posterior horn, and is known as the column of Burdach, posterior ground-bundle, or posterolateral column. It contains principally the shorter tracts, or bundles of longitudinal fibers connecting the adjacent parts of the spinal cord with one another.
Many of the nerve-fibers of the posterior column are the neuraxes of spinal ganglion cells which enter the spinal cord through the posterior roots. The cell-bodies of the spinal ganglion or sen
412 THE CENTRAL NERVOUS SYSTEM.
sory neurones are situated in the spinal ganglia found on the posterior roots of the spinal nerves. In the embryo they are distinctly bipolar, but during further development their two processes approach each other, and then fuse for a certain distance, forming finally single processes which branch like the letter T. In reality, then, there are two processes which are fused for a certain distance from the cell-body of each neurone. The peripherally directed process is regarded as the dendrite of the cell, and the proximal as the neuraxis passing to the spinal cord. The neuraxes enter the spinal cord through the posterior roots and pass to the posterior columns, where they divide, Y-shaped, into ascending and much shorter descending branches, from each of which numerous collateral branches are given off.
From the preceding account of the white matter of the spinal cord, it may be seen that it consists of longitudinally directed neuraxes arranged in so-called short and long tracts or columns. The neuraxes constituting the former, after a short course through the gray matter, emerge from it, and after giving off various collaterals, again penetrate into the gray matter, where their telodendria enter into contact with the ganglion cells. The long columns consist of the neuraxes of neurones the cell -bodies of which are situated in the cerebrum or cerebellum, and of neurones the cell-bodies of which are in the spinal cord or spinal ganglia and the neuraxes of which terminate in the medulla or cerebellum. The nerve-fibers of the various columns give off numerous collaterals which enter the gray matter to end in telodendria. The collaterals of the posterior columns end : (i) between the cells of the gelatinous substance of the posterior horns ; (2) in the columns of Clark ; (3) in the anterior horns, these constituting the principal portion of the so-called reflex bundles ; (4) in the posterior horn of the opposite side. The collaterals of the lateral columns pass horizontally toward the central canal, some ending in the anterior horn, others closely arranged near the columns of Clark, and some arching around the central canal, forming with the corresponding fibers of the other side the anterior bundles of the posterior commissure. The collaterals of the anterior columns form well-marked plexuses in the anterior horns of the same and opposite sides.
We have still to describe the two commissures. The anterior consists of: first, neuraxes from the commissural cells ; second, dendrites from the lateral group of the anterior horn cells ; and, third, the collaterals of the anterolateral column, which end in the gray substance of the other side of the cord. The posterior commissure is probably composed of the collaterals from all the remaining columns. The posterior bundle of this commissure comes from the posterior column ; the middle, from the posterior portion of the lateral column ; and the anterior, or least developed, from the anterior portion of the lateral column, possibly also from the anterior column.
THE CEREBELLAR CORTEX.
413
In the gray commissure, nearer its anterior border, is situated the central canal of the spinal cord, continuous above with the ventricular cavity of the medulla and terminating caudally in the filum terminale. This canal is not patent in the majority of adults, being occluded from place to place. The canal is lined by a layer of columnar cells, developed from columnar cells, known as spongioblasts, lining the relatively larger canal of the embryonic spinal cord. In young individuals these cells are ciliated and their basal portions terminate in long, slender processes in which are embedded neuroglia fibers.
B. THE CEREBELLAR CORTEX,
In the cerebellar cortex we distinguish three general layers the outer molecular, the middle granular (rust-colored layer), and the inner medullary tract.
Blood-vessel.- V- ~
- . " --' * - 41 ^> i
... Nerve-fiber layer.
- - * ... -j^_ _-^
Fig. $30. Section through the human cerebellar cortex vertical to the surface of the convolution. Treatment with M tiller's fluid ; X XI 5 The molecular layer contains three varieties of nerve-cells, those of Purkinje, which border upon the granular layer, the stel
-8
v ?;
I
THE CEREBELLAR CORTEX.
415
late cells, and the small cortical cells. The cells of Purkinje possess a large flask-shaped body (about 60 p. in diameter), from which one or more well -developed dendrites pass toward the periphery. The latter branch freely and the main arborization has in each case the general shape of a pair of deer's antlers. These dendrites extend nearly to the periphery of the cerebellar cortex. In a section horizontal to the surface of the organ the dendrites of the Purkinje's cells are seen to lie in a plane very nearly vertical to the surface of the convolutions, so that a longitudinal section through the latter would show a profile view of the cells. In other words, they have an appearance much like that of a vine trained upon a trellis. The neuraxes of the cells of Purkinje arise from their basal
-* Dendrite.
Cell-body.
Neuraxis.
Fig. 332. Cell of Purkinje from the human cerebellar cortex. Chrome-silver method ; X I2
Neuraxis.
Claw-like telodendrion of dendrite.
Fig. 333. Granular cell from the granular layer of the human cerebellar cortex. Chromesilver method ; X IO
(inner) ends and extend through the granular layer into the medullary substance. During their course they give off a few collaterals,
which pass backward to the molecular layer and end in telodendria
near the bodies of the cells of Purkinje. The stellate cells lie in
various planes of the molecular layer. Their peculiar interest lies
in the character of their neuraxes. The latter are situated in the
same plane as the dendrites of the cells of Purkinje, run parallel to
the surface of the convolution, and possess two types of collaterals.
Those of the first are short and branched ; those of the second
branch at a level with the cells of Purkinje, and form, together
with their telodendria, basket-like nets around the bodies of these
cells. The small cortical cells of the molecular layer are found
4l6 THE CENTRAL NERVOUS SYSTEM.
in all parts of this layer, but are more numerous in its peripheral portion. They are multipolar cells with neuraxes which are not readily stained and concerning the fate of which little is known.
The granular layer contains two varieties of ganglion elements, the so-called granular cells (small ganglion cells) and the large stellate cells. The dendrites of the granular cells are short, few in number (from three to six), branch but slightly, and end in short, claw-like telodendria. Their neuraxes ascend vertically to the surface and reach the molecular layer. At various points some of them are seen to undergo a T-shaped division, the two branches then running parallel to the surface of the cerebellum in a plane vertical to that of the dendrites of the cells of Purkinje. Large numbers of these T-shaped neuraxes produce the striation of the molecular layer of the cerebellum. It is very probable that during their course these parallel fibers come in contact with the dendrites of the cells of Purkinje. The large stellate cells are fewer in number and lie close to the molecular layer, some of them even within this layer. Their dendrites branch in all directions, but extend principally into the molecular layer. Their short neuraxes give off numerous collaterals which end in telodendria among the granular cells.
The medullary substance is composed of the centrifugal neuraxes of the cells of Purkinje and of two types of centripetal neuraxes, the mossy and the climbing fibers. The position of their corresponding nerve-cells is not definitely known. The mossy fibers branch in the granular layer into numerous twigs, and are not uniform in diameter, but are provided at different points with typical nodular swellings. These fibers do not extend beyond the granular layer. The climbing fibers pass horizontally through the granular layer, giving off in their course numbers of collaterals, which extend to the cells of Purkinje, up the dendrites of which they seem to climb.
In the medullary portion of the cerebellum are found a number of groups of ganglion cells known as central gray nuclei. The nerve-cells of these nuclei are multipolar, with numerous, oftbranching dendrites and a single neuraxis.
C THE CEREBRAL CORTEX.
The cell-bodies of the neurones of the cerebrum are grouped in a thin layer of gray matter, varying in thickness from 2 to 4 mm., which, as a continuous sheet, completely covers the white matter of the hemispheres, and in larger and smaller masses of gray matter, known as basal nuclei. In our account of the histologic structure of the cerebral hemispheres we shall confine ourselves in the main to a consideration of the cerebral cortex, the thin layer of gray matter investing the white matter.
THE CEREBRAL CORTEX. 417
From without inward the following layers may be differentiated in the cerebral cortex : (i) a molecular layer ; (2) a layer of small pyramidal cells ; (3) a layer of large pyramidal cells ; (4) a layer of polymorphous cells ; and (5) medullary substance or underlying nerve-fibers.
Aside from neurogliar tissue, we find in the molecular layer a large number of nerve-fibers, which cross one another in all directions, but, as a whole, have a direction parallel with the surface of the brain. Within this layer there are found : (i) the tuft-like telodendria of the chief dendritic processes of the pyramidal cells ; (2) the terminations of the ascending neuraxes, arising mostly from the polymorphous cells ; and (3) autochthonous fibers /. e., those which arise from the cells of the molecular layer and terminate in this layer. The cells of the molecular layer may be classed in three general types polygonal cells, spindle-shaped cells, and triangular or stellate cells. The polygonal cells have from four to six dendrites, which branch out into the molecular layer and may even penetrate into the underlying layer of small pyramidal cells. Their neuraxes originate either from the bodies of the cells or from one of their dendrites, and take a horizontal or an oblique direction, giving off in their course a large number of branching collaterals, which terminate in knob-like thickenings. The spindle=shaped cells give off from their long pointed ends dendrites which extend for some distance parallel with the surface of the brain. These branch, their offshoots leaving them at nearly right angles, the majority passing upward, assuming as they go the characteristics of neuraxes having collaterals. The arborization is entirely within the molecular layer. The triangular or stellate cells are similar to those just described, but possess not two, but three, dendrites. The triangular and spindle-shaped cells, with their numerous dendritic processes resembling neuraxes, are characteristic of the cerebral cortex.
The elements which are peculiar to the second and third layers of the cerebral cortex are the small (about 10 // in diameter) and large pyramidal cells (from 20 //to 30 , in diameter). They are composed of a triangular body, the base of the triangle being downward and parallel to the surface of the brain, of a chief, principal, or primordial dendrite ascending toward the brain-surface, of several basilar dendrites arising from the basal surface of the cell-body, and of a neuraxis which passes toward the medullary substance and which has its origin either from the base of the cell or from one of the basilar dendrites. The ascending or chief dendrite gives off a number of lateral offshoots which branch freely and end in terminal filaments. The main stem of the dendrite extends upward to the molecular layer, in which its final branches spread out in the form of a tuft. The neuraxis, during its course to the white substance, gives off in the gray substance from six to twelve collaterals, which divide two or three times before terminating. 27
4i8
THE CENTRAL NERVOUS SYSTEM.
Aside from the fact that the layer of polymorphous cellt contains a few large pyramidal cells, it consists principally of (i) multipolar cells with short neuraxes (Golgi's cells) and (2) of cells with
Fig. 334. Portions of vertical section of human cerebral cortex, treated by the Golgi
method; X 7- The figure shows the arrangement of the different cells of the cerebral
cortex : gP, Layer of large pyramidal cells ; kF, layer of small pyramidal cells ; pZ, layer
of polymorphous cells (Sobotta, "Atlas and Epitome of Histology").
only slightly branched dendrites and with neuraxes passing toward the surface of the brain (Martinotti's cells). Both these types of cells are, however, not found exclusively in the layer of polymorphous
THE CEREBRAL CORTEX.
419
cells, but may be met with here and there in the layers of the small and large pyramidal cells. The dendrites of the cells of Golgi are projected in all directions, those in the neighborhood of the medullary substance even penetrating into this layer. The neuraxes break up into numerous collaterals, the telodendria of which lie adjacent to the neighboring ganglion cells. The cells of Martinotti, which, as we have seen, occur also in the second and third layers, are either triangular or spindle-shaped. The neuraxis of each cell originates either from the cell-body or from one of its dendrites, and
Brush-like telodendrion
Main dendrite.
Secondary dendrite
Basal dendrite. -^3^
Neuraxis with collaterals.
Fig. 335. Large pyramidal cell from the human cerebral cortex. Chrome-silver
method ; X I 5
ascends (giving off collaterals) to the molecular layer, in which it
finally divides into two or three main branches ending in telodendria. Occasionally it divides in a similar manner in the layer
of small pyramidal cells.
In the medullary substance the following four classes of fibers are recognized : (i) The projection fibers (centrifugal) i. e., those which indirectly connect the elements of the cerebral cortex with the* periphery of the body ; their course may or may not be interrupted
420
THE CENTRAL NERVOUS SYSTEM.
- d
during their passage through the basal nuclei ; (2) the commissural
fibers, which, according to the original definition, pass througli the corpus callosum and anterior commissure, thus joining corresponding parts of the two hemispheres ; (3) the association fibers, which connect different parts of the gray substance of the same hemispheres ; and (4) the centripetal or terminal fibers i.e., the terminal arborizations of those neuraxes, the cells of which lie in some other region of the same or opposite hemisphere, or even in some more distant portion of the nervous system. The projection fibers originate from the pyramidal cells, some of them perhaps from the polymorphous cells. The commissural fibers are also derived from the pyramidal cells, and lie somewhat deeper in the white substance than the association fibers. With the exception of those which join the
cunei and those which lie in the anterior commissure, all the commissural fibers are situated in the corpus callosum. They give off during their passage through the hemispheres large numbers of collaterals, which penetrate at various points into the gray substance and end there in terminal filaments. In this respect their arborization is contrary to the old definition of these fibers, and the latter must be completed by the statement that, besides joining symmetric points of the two hemispheres, they also, by means of their collaterals, may connect other areas of the gray substance with the peripheral regions supplied by their end-tufts (Ramon y Cajal, 93). The association fibers have their origin also in the pyramidal cells. In the medullary substance their neuraxes divide T-shaped, and after a longer or shorter course penetrate into the gray substance of the same hemisphere, where they end as terminal fibers. A few collaterals are, however, previously given off.
Fig. 336. Schematic diagram of the cerebral
cortex : a, Molecular layer with superficial (tangential) fibers ; b, striation of Bechtereff-Kaes ; c,
layer of small pyramidal cells; d, stripe of Baillarger; e, radial bundles of the medullary substance ; y, layer of polymorphous cells.
THE OLFACTORY BULB. 421
which also terminate in the same manner in the gray substance. The association fibers form the bulk of the medullary rays.
On examining a vertical section through one of the cerebral convolutions a number of successive striations may be seen. These are more or less distinct, according to the region, and consist of strands of medullated nerve-fibers between the layers of cells, and parallel with the surface of the convolution. The most superficial form a layer of tangential fibers. Between the molecular layer and the layer of small pyramidal cells is the striation of Bechtereff and Kaes, and in the region of the large pyramidal cells the striation of Baillarger (Gennari) corresponding to the striation of Vicq d'Azyr in the cuneus. In figure 336 the medullary substance is seen below, \vith rays, composed of parallel bundles of fibers, passing upward into the gray substance ; in reality these fibers penetrate much higher than is shown in the illustration.
D. THE OLFACTORY BULB.
The olfactory bulb is composed of five layers, which are especially well marked on its ventral side : first, the layer of peripheral nerve-fibers ; second, the layer of olfactory glomeruli ; third, the stratum gelatinosum, or molecular layer ; fourth, the layer of pyramidal cells (mitral cells) ; and, fifjth, the granular layer with the deeper nerve-fibers.
The layer of peripheral fibers is composed of the nervebundles of the olfactory nerve which cross one another in various directions and form a nerve-plexus. The glomerular layer contains peculiar, regularly arranged, round or oval, and sharply defined structures, which were first accurately studied by Golgi. They are known as glomeruli (from 100 [J. to 300 /JL in diameter), and are in reality complexes of intertwining telodendria. As we shall see, the epithelial cells of the olfactory region of the nose must be regarded as peripheral ganglion cells and their centripetal (basal) processes as neuraxes. The telodendria of these neuraxes, together with those of the dendrites from the mitral or other cells, come in contact with each other within the olfactory glomeruli. The molecular layer consists of small, spindle-shaped ganglion cells. Their neuraxes enter the fifth layer and their short dendrites end in terminal ramifications in the glomeruli. The mitral cells give off neuraxes from their dorsal surfaces which also enter the granular layer, but the majority of their dendrites break up into terminal ramifications in the olfactory glomeruli, as just described. The granular layer (absent in the illustration) is made up of nerve-cells and nerve-fibers ; but, aside from these, we find also large numbers of peculiar cells with a long peripherally and several short centrally directed dendrites. No neuraxes can be demonstrated in these
422
THE CENTRAL NERVOUS SYSTEM.
cells (granular cells). This layer also contains the stellate ganglion cells. The latter are not numerous, but lie scattered, and each possesses several short dendrites and a peripherally directed neuraxis which ends in the molecular layer in a rich arborization. The deep nerve-fibers are grouped into bundles which inclose between them the granular and stellate cells just mentioned. These nerve-fibers
Mitral cells.
Layer of olfactory
glomeruli.
Peripheral nerve-, fibers.
Fig. 337. The olfactory bulb, after Golgi and Ram6n y Cajal. The
not shown.
granular layer is
are derived partly from the neuraxes of the pyramidal or mitral cells and partly from the cells of the molecular layer, while some of them are centripetal fibers from the periphery, which end between the granules of the fifth layer.
E. EPIPHYSIS AND HYPOPHYSIS.
In mammalia the epiphysis, or pineal gland, consists of a fibrous capsule derived from the pia mater, from which numerous fibrous tissue septa and processes pass into the gland, uniting to form quite regular round or oval compartments in which closed follicles or alveoli, whose walls consist of epithelial cells, are found. In the lower portion of the epiphysis there is found a relatively large amount of neuroglia tissue, consisting of coarse fibers, as has been shown by Weigert. The epithelial cells forming the walls of the follicles are of cubic or short columnar shape, and may be arranged in a single layer or may be pseudostratified or stratified. Follicles
EPIPHYSIS AND HYPOPHYSIS. 423
completely filled with cellular elements are found. Other follicles contain peculiar concretions, known as brain-sand or acervulus, of irregular round or oval or mulberry shape. Medullated nerve-fibers have been traced into the epiphysis, but their mode of termination is not known.
The hypophysis, or pituitary body, consists of two lobes. The posterior or infundibular lobe is developed from the floor of the first primary brain-vesicle, and remains attached to the floor of the third ventricle by a stalk, known as the infundibulura ; the anterior or glandular lobe develops from a hollow protrusion derived from the primary oral ectoderm. The distal end of this protrusion or pouch comes in contact with the anterior surface of the lower portion of the infundibulum, and becomes loosely attached to it. As the bones at the base of the skull develop, the attenuated oral end of this pouch atrophies, the distal end becoming finally completely severed from the buccal cavity.
In the infundibular lobe of the hypophysis of the dog, Berkley (94) described three portions presenting different microscopic structure. His account will here be followed :. (i) An outer stratum consisting of three or four layers of cells resembling ependymal cells, which are separated into groups by thin strands of fibrous tissue entering from the fibrous covering of this lobe. (2) A zone consisting of glandular epithelial cells which in certain places are arranged in the form of alveoli, often containing a colloid substance. This zone merges into the central portion, (3), containing variously shaped cells and connective-tissue partitions with blood-vessels. In this portion neurogliar cells (see these) and nerve-cells were stained by the chrome-silver method.
The glandular or anterior lobe resembles slightly in structure the parathyroid. This lobe is surrounded by a fibrous tissue capsule and within it are found variously shaped alveoli or follicles, or, again, columns or trabeculae of cells separated by a very vascular connective tissue. In the alveoli or columns of cells are found two varieties of glandular cells, which may be differentiated more by their staining reaction than by their size and structure, although they present slight structural differences. One variety of cells possesses a protoplasm which shows affinity for acid stains ; these are known as chromophilic cells. They are of nearly round or oval shape, with nuclei centrally placed, and have a protoplasm presenting coarse granules. The other variety of cells, known as chief cells, are more numerous than the chromophilic. They are of cubic or short columnar shape, with nuclei placed in the basal portions of the cells and with protoplasm showing a fine granulation and with an affinity for basic stains. Now and then alveoli containing a colloid substance, similar to that found in the alveoli of the thyroid gland, may be observed. The blood-vessels of the glandular portion are relatively large, the majority of them having only an endothelial lining which comes in contact with the glandular cells.
424 THE CENTRAL NERVOUS SYSTEM.
The circulation of the hypophysis must be regarded as sinusoidal. In the glandular portion of the hypophysis of the dog, Berkley (94) found small varicose nerve-fibers belonging to the sympathetic system. From the larger bundles, which follow the blood-vessels, are given off single fibers, or small bundles of such, which end on the glandular elements in numerous small nodules.
F. GANGLIA*
In the course of peripheral nerves are found numerous larger and smaller groups of nerve-cells, known as ganglia. The neurones of these ganglia are in intimate relation with the neurones of the cen
Fig. 338. Longitudinal section of spinal ganglion of cat.
tral nervous system, and may, therefore, be discussed with the latter. According to the structure and function of their neurones, the ganglia are divided into two groups (i) spinal or sensory ganglia and (2) sympathetic ganglia.
The spinal ganglia are situated on the posterior roots of the spinal nerves. Certain cranial ganglia namely, the Gasserian, geniculate, and auditory ganglia, the jugular and petrosal ganglia of the glossopharyngeal nerves, and the root and trunk ganglia of the vagi are classed with the spinal ganglia, since they present the same structure. The spinal and sensory cranial ganglia are surrounded by firm connective- tissue capsules, continuous with the perineural sheaths of the incoming and outgoing nerve-roots. From
GANGLIA. 425
these capsules connective-tissue septa and trabeculae pass into the interior of the ganglia, giving support to the nerve-elements. The cell-bodies (ganglion cells) of the neurones constituting these ganglia are arranged in layers under the capsule and in rows and groups or clusters between the nerve-fibers in the interior of the ganglia. More recent investigations have shown that several types of neurones are to be found in the spinal and cranial sensory ganglia ; of these, we may mention the following : (i) Large and small unipolar cells with T- or Y-shaped division of the process. These neurones, which constitute the greater number of all the neurones of the ganglia under discussion, consist of a round or oval cell-body, from which arises by means of an implantation cone
Fig. 339. Ganglion cell from the Gasserian ganglion of a rabbit ; stained in methylene
blue (intra vitani).
a single process, which, soon after it leaves the cell, becomes invested with a medullary sheath and usually makes a variable number of spiral turns near the cell-body. According to Dogiel, this process divides into two branches, usually at the second or third node of Ranvier, sometimes not until the seventh node is reached. Of these two branches, the peripheral is the larger, and enters a peripheral nerve-trunk as a medullated sensory nerve-fiber, terminating in one of the peripheral sensory nerve-endings previously .described. The central process, the smaller of the two, becomes a medullated nerve-fiber, which enters the spinal cord or medulla in a manner described in a former section. The cell-body of each of these neurones is surrounded by a nucleated capsule, continuous with
426
THE CENTRAL NERVOUS SYSTEM.
the neurilemma of the single process. (2) Type II spinal ganglion cell of Dogiel. Dogiel has recently described a second type of spinal ganglion cell which differs materially from the type just described. The cell-bodies of these neurones resemble closely those of the typical spinal ganglion neurones. Their single medullated processes divide, however, soon after leaving the cells into branches which divide further and which do not pass beyond the bounds of the ganglia but terminate, after losing their medullary sheaths, in complicated pericapsular and pericellular end-plexuses surrounding the capsules and cell-bodies of the typical spinal ganglion cells. (3) Multipolar ganglion cells ; in nearly all spinal and cranial ganglia there are found a few multipolar nerve-cells, which in shape and structure resemble the nerve-cells of the sympathetic system.
Fig. 340. Diagram showing the relations of the neurones of a spinal ganglion ;
p. r., posterior root; a. r., anterior root; /. s., posterior branch and a. s., anterior
branch of spinal nerve ; w. r., white ramus communicans ; a, large, and 6, small spinal
ganglion cells with T-shaped division of process ; c, type II spinal ganglion cells (Dogiel);
s, multipolar cell ; d, nerve-fiber from sympathetic ganglion terminating in pericellular
plexuses (slightly modified from diagram given by Dogiel).
Entering the spinal ganglia from the periphery are found a relatively small number of small, medullated or nonmedullated nervefibers, probably derived from sympathetic ganglia. These nervefibers, medullated and nonmedullated, the former losing their medullary sheaths within the ganglia, approach a spinal ganglion cell, and after making a few spiral turns about its process, terminate in pericapsular and pericellular end-plexuses. Dogiel believes that the cell-bodies and capsules thus surrounded by the terminal branches of the sympathetic fibers terminating in the spinal ganglia belong to the spinal ganglion cells of the second type first described by him. In figure 340 is represented by way of diagram the structure of a spinal ganglion.
In the medium-sized cells (from 30 fJ. to 45 fj. in diameter) of the
GANGLIA. 427
spinal ganglia of the frog, von Lenhossek (95) found centrosomes surrounded by a clear substance (centrospheres). The entire structure lay in a depression of the nucleus and contained more than twelve extremely minute granules (centrosomes), which showed a staining reaction different from that of the numerous concentrically laminated granules present in the protoplasm. This observation is interesting in that it proves that centrosome and sphere occur also in the protoplasm of cells which have not for a long time undergone division and in which there is no prospect of future division.
Sympathetic Ganglia. The ganglia, of the sympathetic nervous system comprise those of the two great ganglionated cords, found on each side of the vertebral column and extending from its cephalic to its caudal end, with which may be grouped certain cranial ganglia having the same structure, namely, the sphenopalatine, otic, ciliary, sublingual, and submaxillary ganglia ; also three un
Fig. 341. Neurone from inferior cervical sympathetic ganglion of a rabbit; methylene blue stain.
paired aggregations of ganglia, found in front of the spinal column, of which the cardiac is in the thorax, the semilunar in the abdomen, and the hypogastric in the pelvis ; and further, large numbers of smaller ganglia, the greater number of which are of microscopic size and are found in the walls of the intestinal canal and bladder, in the respiratory passages, in the heart, and in or near the majority of the glands of the body.
The sympathetic ganglia are inclosed in fibrous tissue capsules continuous with the perineural sheaths of their nerve-roots. The thickness of the capsule bears relation to the size of the ganglion, being thicker in the larger and thinner in the smaller ones. From these capsules thin connective-tissue septa or processes pass into the interior of the ganglia, supporting the nerve elements.
The sympathetic neurones, the cell-bodies and dendritic processes of which are grouped to form the sympathetic ganglia, are variously
428 THE CENTRAL NERVOUS SYSTEM.
shaped unipolar, bipolar, and multipolar cells, the cell-bodies of which are surrounded by nucleated capsules, continuous with the neurilemma of their neuraxes. In the sympathetic ganglia of mammalia and birds the great majority of sympathetic neurones are multipolar, although in nearly all ganglia a small number of bipolar and unipolar cells are to be found, usually near the poles of the ganglia.
The dendrites of the sympathetic neurones in any one ganglion branch repeatedly. Of these branches, some extend to the periphery of the ganglion, where they interlace to form a peripheral subcapsular plexus, while others interlace to form plexuses between the cell-bodies of the neurones in the interior of the ganglion
O O
pericellular plexuses. These pericellular plexuses are external to the capsules surrounding the cell-bodies of the sympathetic neurones.
Fig. 342. From section of semilunar ganglion of cat ; stained in methylene-blue, intra
vitam (Huber, Journal of Morphology, 1899).
The neuraxes of the sympathetic neurones, the majority of which are nonmedullated, the remainder surrounded by delicate medullary sheaths, arise from the cell-bodies either from implantation cones or from dendrites at variable distances from the cellbodies, leave the ganglion by way of one of its nerve-roots, and terminate in heart muscle tissue, nonstriated muscle, and glandular tissue, and to some extent in other ganglia, both sympathetic and spinal. Terminating in all sympathetic ganglia are found certain small medullated nerve-fibers, varying in size from about 1.5 // to 3 fjt. The researches of Gaskell, Langley, and Sherrington have shown that these small medullated nerve-fibers leave the spinal cord through the anterior roots of the spinal nerves from the first dorsal to the third or fourth lumbar and reach the sympathetic
GANGLIA.
429
ganglia through the white rand comnmnicantes. Similar small medullated nerve-fibers are found in certain cranial nerves. These small medullated nerve-fibers, which may be spoken of as white rami fibers, after a longer or shorter course, in which they may pass through one or several ganglia without making special connection with the neurones contained therein, terminate in some sympathetic ganglion in a very characteristic manner. After entering the sympathetic ganglion in which they terminate, they branch repeatedly while yet medullated. The resulting branches then lose their medullary sheaths and divide into numerous small, varicose nerve -fibers, which interlace to form intracapsular plexuses, which surround the cell-bodies of the sympathetic neurones. In the sympathetic ganglia of mammalia such intracapsular pericellular
Fig. 343. From section of stellate ganglion of dog, stained in methylene-blue and alum
carmin : a, white ramus fiber ( Huber, Journal of Morphology, 1899).
plexuses may be very simple, consisting of only a few varicose nerve-fibers, or very complicated, consisting of many such fibers. In the sympathetic ganglia of reptilia, in which are found very large sympathetic neurones, the white rami fibers are wound spirally about the cell-bodies of such neurones before terminating in complicated pericellular plexuses. In the frog and other amphibia the sympathetic neurones are unipolar nerve-cells. The white rami fibers terminating in the sympathetic ganglia of amphibia are wound spirally about the single processes of these unipolar cells while yet medullated fibers, but they lose their medullary sheaths before terminating in the intracapsular pericellular plexuses. From what has been said concerning the white rami fibers and their relation to the sympathetic neurones, it is evident that the sympathetic neu
430
THE CENTRAL NERVOUS SYSTEM.
rones, the cell-bodies and dendrites of which are grouped to form the sympathetic ganglia, form terminal links in nerve or neurone chains ; the second link of these chains is formed by neurones the cell-bodies of which are situated in the spinal cord or medulla, the
Fig. 344. From section of sympathetic ganglion of turtle, showing white rami
fibers wound spirally about a large process of a unipolar cell, and ending in pericellular
plexus (Huber, Journal of Morphology, 1899).
neuraxes leaving the cerebrospinal axis through the white rami as small medullated nerve-fibers, which terminate in pericellular plexuses inclosing the cell-bodies of the sympathetic neurones.
Large medullated nerve -fibers, the dendrites of spinal ganglion neurones, reach the sympathetic ganglia through the white rami.
Fig. 345. From section of sympathetic ganglion of frog, showing spiral fiber (white ramus
fiber) and pericellular plexus (Huber, Journal of Morphology, 1899).
They make, however, no connection with the sympathetic neurones, but pass through the ganglia to reach the viscera, where they terminate in special sensory nerve-endings or in free sensory nerveendings.
RELATIONSHIP OF NEURONES. 43 I
G. GENERAL SURVEY OF THE RELATIONS OF THE
NEURONES TO ONE ANOTHER IN THE
CENTRAL NERVOUS SYSTEM.
The following figures illustrate the modern theories with regard to the relationship of the neurones in a sensorimotor reflex cycle. The pathway along which the impulse from the stimulated area of the body is transmitted to the motor nerve end-organ traverses two neurones (primary neurones) which are in contact by means of their telodendria situated within the gray matter of the spinal cord. The cell-body of the sensory neurone lies within the spinal ganglion ; that of the motor neurone, in the anterior horn of the spinal cord. The dendrite of the sensory neurone commences
mN
Fig- 346. Schematic diagram of a sensorimotor reflex arc according to the modern
neurone theory ; transverse section of spinal cord : mN, Motor neurone ; sN, sensory
neurone ; C 1 , nerve-cell of the motor neurone ; C 2 , nerve-cell of the sensory neurone ;
d, dendrite ; n, neuraxis of both neurones ; f, telodendria ; M, muscle-fiber ; A, skin
with peripheral telodendrion of sensory neurone.
as a telodendrion in the skin or perhaps also in more deeply seated structures, and transmits a cellulipetal impulse, while its cellulifugal neuraxis and telodendrion (the latter in the gray matter of the cord) transfer the impulse to the cellulipetal telodendrion of the motor neurone. The cellulifugal neuraxis of the latter finally ends as a telodendrion in the muscle. (Figs. 346 and 347.)
In the case of longer tracts the conditions are somewhat more complicated, as, for instance, in tracing the impulse along the sensory fibers to the cortex of the brain, and from there along the motor fibers to the responding muscle. In such cases secondary neurones are called into play by means of their telodendria, which are necessarily in contact with the primary neurones just described.
432
THE CENTRAL NERVOUS SYSTEM.
When we take into consideration the simplest possible case, that of the motor segment of such a neurone-chain, we find, for instance (Fig. 348), that the neuraxis of a pyramidal cell in the brain cortex (psychic cell) enters the white substance and traverses it as a nervefiber through the peduncle and the pyramid into the crossed pyramidal tract of the opposite side. Here its telodendria come in contact with those of the motor neurone of the anterior horn.
In the foregoing instance the motor nerve tract is composed of two neurones of a motor neurone of the first order, extending from the cortex of the brain to the anterior cornua of the spinal cord, and of a motor neurone of the second order, the elements of which extend from the anterior cornua to the telodendria in the muscle.
Fig. 347. Schematic diagram of a sensorimotor reflex cycle ; sagittal section of
the spinal cord: C 1 , Motor cells of the anterior cornua; , , neuraxes ; sN, sensory
neurone ; C 2 , spinal ganglion cell ; C, collaterals of the sensory neuraxes ; </, dendrite of
sensory neurone ; the broken lines at the cells on the left indicate their dendrites.
The sensory tract may likewise be composed of neurones of the first and second orders. The cellulifugal neuraxis arising from a cell of the spinal ganglion passes to the posterior column of the cord, gives off collaterals to the latter, and then passes upward by means of its ascending branch through the posterior column to the medulla. Although here the relationship is not so clearly defined as in the motor tract, it may nevertheless be assumed that the cellulifugal (but centripetally conducting) neuraxis at some point or other terminates in telodendria (sensory neurone of the first order), which enter into contact with the corresponding structures of a cell of the spinal cord or medulla oblongata. These cells would then
RELATIONSHIP OF NEURONES.
433
constitute the sensory neurones of the second order. Exactly how their cellulifugal neuraxes end has not as yet been fully determined, but it is very probable that in this case the telodendria are represented by the coarse end-fibers which penetrate into the brain cortex, and here seem to come in contact with the dendrites of the pyramidal cells.
Fig. 348 Schematic diagram of the reflex tracts between a peripheral organ and the brain cortex: H, Cerebral cortex; mJV 1 , motor neurone of the first, sJV 2 , sensory neurone of the second, degree ; C 1 , motor cell of the spinal cord ; C 2 , sensory cell of a spinal ganglion ; C 3 , pyramidal cell of the brain cortex (pyschic cell) ; C 4 , nerve-cell of a sensory neurone of the second degree ; , n, n, n, neuraxes ; </, d, dendrites ; f, c, c, c, collaterals; /, t, telodendria; sJV 1 , sensory neurone first degree; mJV*, motor neurone second degree.
28
434
THE CENTRAL NERVOUS SYSTEM.
H. THE NEUROGLIA.
The neuroglia tissue is an especially differentiated supporting tissue found in the central nervous system, the optic chiasm, optic nerve and retina and for some distance, at least, in the olfactory nerve. Its relation to other tissues has long been a matter of controversy, but modern observers have shown quite conclusively that neuroglia tissue is of ectodermal origin. It should not be understood, however, that the neuroglia tissue forms the only supporting tissue of the central nervous system. In all parts of the central nervous system, more especially, however, in the spinal cord, there is found true connective tissue of mesoblastic origin, more especially in connection with the blood-vessels.
At an early stage of embryonic development there are seen in the spinal cord, and also in the brain, elements radially disposed around the neural canal, which upon closer observation appear to be processes emanating from the epithelial cells lining the neural canal. These processes may undergo repeated dichotomous division, ending finally in a swelling near the periphery of the cord. These cells are known as ependymal cells, and are differentiated from ectodermal cells, called spongioblasts. In later stages the radial arrangement is still preserved, but the cell-bodies no longer all border upon the central canal, many being found at varying distances from the latter. At this stage in the development of the spinal cord, the elements retaining their original characteristics are situated only in the region of the ventral and dorsal fissures of the spinal cord, and during further development increase in number.
These observations would seem to indicate that at least a
portion of the neurogliar cells, which develop from the ependymal cells previously mentioned, originate from the epithelium of the central canal, and that from here they are gradually pushed toward the periphery of the cord. This assumption is still further strengthened by the fact that later the epithelial cells of the central canal still continue to divide. Later observations (Schaper, 97) show, however, that neurogliar cells develop also from certain undifferentiated germinal cells of the neural canal, of ectodermal origin,, which
Fig. 349. Neurogliar cells : <?, From
spinal cord of embryo cat ; 6, from brain of
adult cat ; stained in chrome-silver.
THE NEUROGLIA. 435
wander from their position near the neural canal toward the periphery of the medullary tube, where they develop into neuroglia cells.
Owing to the fact that of the several methods now at hand for studying neuroglia tissue no two give identical results, the views concerning this tissue are still at variance. The Golgi or chromesilver method was for many years the only method by means of which the elements of neuroglia tissue were brought to light with any degree of clearness. In preparations of the central nervous system treated with this method all the neuroglia elements appear as cells with processes. The cell bodies of these cells as also the processes being stained black or nearly black (as seen with transmitted light) so that the relations of the processes to the cellular constituents can not be ascertained, investigators who have made use of this method in their study of neuroglia distinguish two essentially different cellular elements of the neuroglia: ependymal cells, previously mentioned, and neuroglia cells, so-called spider cells or astrocytes. The astrocytes are grouped under two main heads : short-rayed astrocytes, possessing a few shart processes, found in the gray matter, and long-rayed astrocytes with many fine and long processes, which do not appear to branch, found both in the gray and white matter. The two types of astrocytes are not clearly defined, as intermediate types are also found. In figure 349 are shown two astrocytes (long-rayed) as seen in chrome-silver preparations.
A number of investigators have in recent years perfected methods by means of which neuroglia tissue could be stained differentially Weigert, Mallory, Benda. In tissues treated after any one of these rather complicated differential staining methods the processes of the neuroglia cells as seen in chrome-silver preparations appear in the form of well-contoured fibrils, which are not interrupted by the cellbodies of the neuroglia cells, from which they are either entirely separated or are seen to pass through the protoplasm of the cells without losing their identity. In preparations of the central nervous system stained after Benda's differential neuroglia tissue staining method, numerous neuroglia cells may be observed both in the gray and white matter. Certain of these cells possess very little protoplasm, others and these are in the majority present it to an appreciable extent. The shape of such cells varies. When situated in the main mass of the white matter of the spinal cord, and seen in cross-sections of the cord, they present an irregular triangular and quadrangular form, with protoplasmic branches which arise from the angles and which extend for a variable distance between the nervefibers. In such preparations it may be seen that the neuroglia fibers pass in close proximity to the neuroglia cells, apparently embedded in the outermost part of their protoplasm, and often following the protoplasmic processes. This view of the structure of neurogliar tissue is more in accord with recent investigations on this
436
THE CENTRAL NERVOUS SYSTEM.
subject (Weigert, Mallory, Benda, Krause, Hardesty, Huber). In figure 350 are shown two neuroglia cells from a cross-section of a human spinal cord, in which the relation of neuroglia fibers to neuroglia cells is shown.
Fig. 350. Typical neuroglia cells, from cross-section of the white matter of the
human spinal cord, stained after Benda' s selective neuroglia tissue staining method;
X 1 200 (Huber, "Studies on Neuroglia Tissue," Vaughan Festschrift, 1903).
L THE MEMBRANES OF THE CENTRAL NERVOUS SYSTEM.
The membranes of the central nervous system (meninges) are three in number: the outer,' or dura mater ; the middle, or arachnoid; and the inner, or pia mater.
Around the brain the dura mater is very intimately connected with the periosteum and presents a smooth inner surface. It consists of an inner and an outer layer, the two being separated from each other only in certain regions. At such points either the inner layer is pushed inward to form a duplicature, as in the falx cerebri and falx cerebelli, tentorium, and diaphragma sellae, or the outer layer is pushed outward to form small, blindly ending sacs. The venous and lymphatic sinuses lie between the two layers. The outer
THE MEMBRANES OF THE CENTRAL NERVOUS SYSTEM. 437
layer of the dura is continued some distance along the cerebrospinal nerves.
The dura mater of the spinal cord does not form the periosteum for the bones forming the vertebral canal ; these possess their own periosteum. The spinal dura mater is covered on its outer surface by a layer of endothelial cells and is separated from the wall of the vertebral canal by the epidural space, containing a venous plexus imbedded in loose areolar connective tissue and adipose tissue.
The dura consists chiefly of connective-tissue bundles having a longitudinal direction along the spinal cord. Within the cranium, however, the bundles of the inner and outer layers cross each other ; those of the outer having a lateral direction anteriorly and a mesial posteriorly ; those of the inner, a mesial direction anteriorly and a lateral posteriorly. In the falx cerebri, tentorium, etc., the fibers are arranged radially, extending from their origin toward their borders. The shape and size of the connective-tissue cells vary greatly, and their processes form a network around the bundles of connective tissue. Few elastic fibers are present, and, according to K. Schultz, these are entirely absent in the new-born ; they are somewhat more numerous in the dura of the spinal cord. The dura is very rich in blood-capillaries, and the presence of lymphatic channels in communication with the subdural space may be demonstrated by means of puncture-injections. The inner surface of the dura mater is covered by a layer of endothelial cells.
The dura mater is quite richly supplied with nerves, especially in certain regions. These are of two varieties : (i) Vasomotor fibers, which form plexuses in the adventitial coat of the arteries, and would seem to terminate in the muscular coat of the arteries ; (2) medullated nerve-fibers, which either accompany the blood-vessels in the form of larger or smaller bundles or have a course independent of the vessels. After repeated division these medullated nerve-fibers lose their medullary sheaths and terminate between the connective-tissue bundles in fine varicose fibrils, which -may often be traced for long distances (Huber, 99).
The arachnoid is separated from the dura by a space which is regarded as belonging to the lymphatic system the subdural space. The outer boundary of the arachnoid consists, as does the inner lining of the dura, of a layer of flattened endothelial cells. The arachnoid is made up of a feltwork of loosely arranged connective-tissue trabeculse, which also penetrate into the lymph-space between it and the pia the subarachnoid space. For a short distance from their points of origin the cerebrospinal nerves are accompanied by arachnoid tissue. In the brain the arachnoid covers the convolutions and penetrates with its processes into the sulci. These processes are especially well developed in the so-called cisterns ; in the cisterna cerebellomedullaris, fossae Sylvii, etc. In the spinal cord the subarachnoid space is separated by the ligamenta denticulata into two large communicating spaces a dorsal and a ven
438
THE CENTRAL NERVOUS SYSTEM.
Gray matter.
tral. The dorsal space is further divided by the septum posticum, best developed in the cervical region.
At certain points, usually along the superior longitudinal sinus, the outer surface of the arachnoid is raised into villi, which are covered by the inner layer of the dura, and form with the latter the Pacchionian bodies or granulations. These villi are connected with the arachnoid by pedicles so delicate that they often seem to be suspended free in the venous current of the sinus.
The subarachnoid space contains numerous blood-vessels, some of which are free and others attached to the arachnoid. Their adventitta is covered by endothelium ; hence the subarachnoid space
would seem to assume here the character of a perivascular space.
The trabeculse and membranes composing the arachnoid tissue show a great similarity to those of the mesentery, and especially to those of the omentum. The whole constitutes a typical areolar connective tissue, interrupted at numerous points and covered by a continuous layer of endothelial cells. Large numbers of spiral fibers are found here twining around single or groups of connective-tissue fibers. The arachnoid possesses neither bloodvessels nor nerves.
The pia mater covers the entire surface of the brain and spinal cord, dipping down into every fissure and crevice. In the spinal cord it consists of an outer and an inner lamella, the former being composed of bundles of connective tissue containing elastic fibers. As a rule, the course of the fibers is longitudinal. Externally this layer is covered by a layer of endothelium. The bloodvessels lie between the outer and inner layers of the pia. The inner layer (pia intima) is made up of much finer elements, and is covered on both sides by endothelium. It is this layer which accompanies the blood-vessels penetrating into the spinal cord, surrounding their adventitia and forming with the latter the limits of their perivascular spaces. These are in communication with the
White
matter.
Fig. 351. Section through the cerebral cortex of a rabbit. The blood-vessels are injected ; X 4
BLOOD-VESSELS OF THE CENTRAL NERVOUS SYSTEM. 439
interpial spaces, and, by means of the adventitia of the blood-vessels, with the subarachnoid space. Aside from those just described, numerous fine, nonvascular, connective-tissue septa penetrate from the pia mater into the substance of the spinal cord. Wherever the pia mater penetrates the spinal cord, the latter is hollowed out, forming the so-called pial funnels. Just beneath the pia there is found in the spinal cord of man a well-developed layer of neuroglia fibers. The posterior longitudinal septum of the spinal cord consists (in the thoracic region) exclusively of neurogliar elements, but in the cervical and lumbar regions the pia also enters into its peripheral formation.
In the brain, however, the conditions are somewhat different. Here the external layer of the pia disappears, leaving only a single layer analogous to the pia intima of the spinal cord.
The pia mater enters into the formation of the choroid plexus. This structure consists of numerous freely anastomosing bloodvessels, which form villus-like processes, the surfaces of which are covered by squamous or cubic epithelial cells. This epithelium is regarded as a continuation of the ventricular epithelium, and is ciliated, at least in embryonic life and in the lower classes of vertebrates. From an embryologic point of view the whole structure represents the brain-wall reduced to a single layer of epithelium (internal epithelial investment) pushed forward into the ventricle by the vessels and pia mater.
Since the dura and arachnoid accompany the cerebrospinal nerves for some distance, it is obvious that the lymph-vessels of the nasal mucous membrane (see these) may also be injected from the subarachnoid space (compare also Key and Retzius).
The pia mater, like the dura mater, receives two varieties of nerve-fibers : (i) Vasomotor fibers, which form plexuses in the adventitial coat of the arteries and terminate in the muscular layer of the arteries. These may be traced to the small precapillary branches of the vessels. (2) Larger and smaller bundles of relatively large, medullated nerve-fibers, which accompany the larger pial vessels, forming loose plexuses in or on the adventitial coat of the vessels. After repeated divisions these medullated nerves lose their medullary sheaths and terminate in the adventitia of the vessels, in long, varicose fibrils or in groups of such fibrils (Huber,
9.9)
J. BLOOD-VESSELS OF THE CENTRAL NERVOUS
SYSTEM,
The blood-vessels of the central nervous system present certain peculiarities which deserve special consideration.
The spinal cord receives its arterial blood mainly through vessels which accompany the spinal nerve roots and through numerous anastomoses from a plexus in the pia mater in which there may be
44O THE CENTRAL NERVOUS SYSTEM.
recognized a median ventral unpaired line of anastomosis and along each half of the spinal cord four other lines of anastomosis. From the median unpaired line of anastomosis some 200 to 2 50 branches pass into the anterior fissure, each of which generally divides into a right and left branch just in front of the commissure, each branch being distributed to the gray matter in its immediate vicinity. The white matter receives its blood-supply from vessels of the plexus in the pia mater, from which numerous fine branches are given off which terminate in capillary networks and extend as far as the gray matter. The veins return the blood to the veins of the pia mater, following in the main the course of the arteries. The central and peripheral arteries do not anastomose except through capillaries and now and then precapillaries (Adamkiewicz and Kadyi).
In the cerebral cortex the capillaries are particularly numerous, and are closely meshed wherever groups of ganglion cells occur. In the medullary substance they are somewhat less closely arranged, their meshes being oblong. In the cerebellum the arrangement is analogous. Of all the layers composing the cerebellum the granular is the most vascular ; within it the capillaries are also densely arranged and form a close network.
Lymphatic vessels with definitive walls have thus far not been discovered in the central nervous system. The blood-vessels through the central nervous system are, however, surrounded by perivascular spaces, which may be regarded as performing the function of lymphatic vessels.
TECHNIC.
The organs of the central nervous system are best fixed in Miiller's fluid, washed with water, cut in celloidin, and stained with carmin. Such preparations are suitable for general topographic work.
Special structures as, for instance, the medullary sheaths of the nervefibers, the ganglion cells, the relations of the different neurones and dendrites to one another, etc. require different treatment.
The medullary sheath may be demonstrated as follows (Weigert): Pieces of tissue (spinal cord, for instance), fixed as usual in Miiller's or Erlicki's fluid, are transferred without washing to alcohol, imbedded in celloidin, and cut. Before staining the sections it is necessary to subject them to the mordant action of a neutral copper acetate solution (a saturated solution of the salt diluted with an equal volume of water). The sections may be subjected to the mordant action of this solution, but the following procedure is more convenient : The specimens, imbedded in celloidin and fastened to a cork or a block of wood, are placed for one or two days in the copper solution just described. At the expiration of this time the pieces of tissue will have become dark, and the surrounding celloidin light green. They are then placed in 80% alcohol, in which they may be preserved for any length of time. The sections are then stained in the following solution : i gm. of hematoxylin is dissolved in 10 c.c. absolute alcohol, and 90 c.c. of distilled water are then added (the fluid must remain exposed to the air for a few days) ; the addition of an alkali as, for instance, a cold satu
TECHXIC. 441
rated solution of lithium bicarbonate (i. c.c. to 100 c.c. of hematoxylin solution) brings out the staining power of the solution at once. In this stain the sections are placed (at room -temperature) for a day, and then in a thermostat (40 C.) for a few hours. The sections, now quite dark, are washed in distilled water and then placed in the so-called differentiating fluid. The latter consists of borax 2 gm., ferrocyanid of potassium 2.5 gm., and distilled water 100 gm. In this fluid the color of the sections is differentiated by virtue of the circumstance that the medullary sheath retains the dark stain, while the remaining structures, such as the ganglion cells, etc. , are bleached to a pale yellow. The time required for this differentiation varies, but it is usually complete at the end of a few minutes. The sections are then washed in distilled water, dehydrated in alcohol, cleared in carbol-xylol (carbolic acid i part, xylol 3 parts) and mounted in balsam.
Weigert's new method is more complicated, but fruitful of correspondingly better results. The preliminary treatment remains the same. After the tissues have been imbedded in celloidin and this hardened in 80 % alcohol, they are transferred to a mixture composed of equal parts of a cold saturated aqueous solution of neutral copper acetate and 10% aqueous solution of sodium and potassium tartrate, and the whole is placed in the thermostat. Larger pieces as, for instance, the pons Varolii of man may remain in the solution longer than twenty-four hours, after which time, however, the mixture must be changed ; but in no case should the specimens be permitted to remain longer than forty -eight hours in this solution. The temperature in the thermostat should not be high, otherwise the specimens will become brittle. The objects are now placed in a simple aqueous solution of neutral copper acetate, either saturated or half diluted with water, and again put in the oven. They are then rinsed in distilled water and placed in 80 % alcohol ; after remaining in this for one hour, they are in a condition to cut, but may be preserved still longer if desired. Cut and stain in the customary manner. The staining solution is prepared as follows : (0) lithium carbonate 7 c.c. and distilled water 93 c.c. (saturated aqueous solution) ; (<) hematoxylin I gm. , absolute alcohol 10 c.c. ; both a and b keep for some time, and may be kept on hand as stock solutions. Shortly before using, 9 parts of a and i part of b are mixed. After remaining in this solution for from four to five hours at room -temperature the sections are well stained, but do not overstain even if allowed to remain in the solution for twenty-four hours. In the case of loose celloidin sections the use of the differentiating fluid is superfluous. Hence this method is particularly advantageous when the gray and the white matter can not be distinguished macroscopically. Finally, the sections are washed in water, placed in 95% alcohol, cleared with carbol-xylol or anilin-xylol (in the latter case carefully washed with xylol), and mounted in xylol -balsam. The medullated fibers appear dark blue to black, the background pale or light pink, and the celloidin occasionally bluish. In order to remove the latter color, it is only necessary to wash the sections in 0.5% acetic acid instead of ordinary water ; a process, however, not to be recommended in the case of very delicate preparations as, for instance, the cerebral cortex. In applying Weigert's methods a certain thickness of section (not exceeding 25 i^ is essential, since in thicker sections the medullary sheaths are not sharply differentiated from the surrounding tissue.
44 2 THE CENTRAL NERVOUS SYSTEM.
For thick sections the modified Weigert method, or Pal's method, is employed. After the specimens have been treated according to Weigert's method up to the point of staining with hematoxylin, they are placed for from twenty to thirty minutes in a 0.25% solution of potassium permanganate. As differentiating fluid a solution of oxalic acid i gm., potassium sulphite i gm., and water 200 c.c. is used, care being taken, as in the case of Weigert' s differentiating fluid, that the gray matter is thoroughly bleached (here entirely colorless) and the white matter dark. By this method the medullary sheaths are stained blue, while the rest of the structure remains colorless. The staining is very precise, but not so intense as by Weigert' s method. Hence its adaptability for thicker sections.
Benda's method is a modification of the Weigert-Pal methods. The tissues are hardened in Miiller's or Erlicki's fluid, imbedded in celloidin, and cut. The sections are then subjected to the action of the following mordant for from twelve to twenty-four hours : liquor ferri ter sulphatis i part, distilled water 2 parts. They are then thoroughly rinsed in two tap-waters and one distilled water and then stained in the following hematoxylin solution: hematoxylin i gm., absolute alcohol 10 c.c., distilled water 90 c.c.; in which they remain for twenty-four hours. They are next washed in tap -water for from ten to fifteen minutes and treated with a 0.25% aqueous solution of permanganate of potassium until the gray and the white matter are differentiated, after which they are rinsed in distilled water and bleached in the following solution until the gray matter has a light yellow color : hydric sulphite 5 to 10 parts, distilled water 100 parts. The sections are then washed in tap -water for from one to two hours, rinsed in distilled water, dehydrated, cleared in carbol-xylol, and mounted in balsam. Medullary sheaths will be stained a bluish-black ; other structures, a light yellow. Sections stained after the Weigert, Pal, or Benda method may be counterstained in Van Gieson's picric-acidfuchsin stain (i% aqueous solution of acid fuchsin, 15 parts; saturated aqueous solution of picric acid, 50 parts ; distilled water, 50 parts) . The fibrous connective tissue in the sections and degenerated areas stains a light red.
Apathy (97) demonstrates the fibrillar elements of the nervous system in invertebrates and vertebrates by means of his gold method. Fresh tissue may be used, or tissue already fixed. In the first case thin membranes are placed for at least two hours in a i <f solution of yellow chlorid of gold in the dark, then carried over without washing into a i % solution of formic acid (sp. gr. 1.223), an d finally exposed for from six to eight hours to the light (the formic acid may have to be changed). These specimens are best mounted directly in syrup of acacia or in concentrated glycerin. In his second method Apathy fixes vertebrate tissues for twenty-four hours in sublimate-osmic acid (i vol. saturated solution of corrosive sublimate in 0.5% sodium chlorid solution combined with i vol. 1% osmic acid solution), washes repeatedly in water, and places for twelve hours in an aqueous iodo-iodid of potassium solution (potassium iodid i Jc and iodin 0.5%). The further treatment is the same as after ordinary corrosive sublimate fixation. Finally,' the specimens are imbedded in paraffin with the aid of chloroform, cut, and mounted by the water method. The whole process, up to the point of imbedding in paraffin, is carried out in the dark. The sections are then passed through chloro
TECHNIC. 443
form and alcohol into water, where they are allowed to remain for at least six hours ; or they may be washed in water, placed for one minute in i % formic acid, again washed in water, immersed for twenty-four hours in a i <f solution of gold chlorid, rinsed in water, and finally placed in a i / formic acid solution and exposed to the light. For the latter purpose glass tubes are employed in which the slides are placed obliquely, with the sections downward. A uniform illumination of the section with "as intense a light and low a temperature " as possible are conditions indispensable to the attainment of successful results. The sections are then again washed in water and mounted in glycerin or syrup of acacia, or in Canada balsam after being dehydrated. Thin membranes are stretched upon small frames of linden wood especially prepared for this purpose. Their further treatment is then the same as that of sections fixed to the slide. If successful, the nerve-fibrils appear dark violet to black. The large ganglia in the spinal cord of lophius, the calf, etc., are especially recommended as appropriate vertebrate material.
Bethe (1900) has recommended the following method for staining neurofibrils and Golgi-nets in the central nervous system of vertebrates:
The perfectly fresh tissue is cut in thin lamellae, varying in thickness from 4 to 10 mm. These are placed on pieces of filter-paper and then in 3 to 7-5% nitric acid, in which they remain twenty-four hours. From the hardening fluid the pieces of tissue are transferred into 96% alcohol, where they remain for from twelve to twenty-four hours. They are then placed in a solution of ammonium -alcohol, ammonium (sp. gr. 0.95 to 0.96), i part; distilled water, 3 parts ; 96% alcohol, 8 parts, in which they remain for from twelve to twenty-four hours. The temperature of this solution should not exceed 20 C. The tissues are then placed for from six to twelve hours in 96% alcohol, and next in a hydrochloric acid-alcohol solution, concentrated hydrochloric acid (sp. gr. 1.18 37%), i part; distilled water, 3 parts; and 96% alcohol, 8 to 12 parts, in which they remain for several hours. The temperature of this solution should not exceed 20 C. The tissues are then again placed in 96% alcohol for frofri ten to twenty-four hours, and next in distilled water for from two to six hours. The tissues are now placed for twenty-four hours in a 4% aqueous solution of ammonium molybdate. (This solution should be kept at a temperature varying from 10 to 15 C., if it is desired to stain the neurofibrils ; or at a temperature varying from 10 to 30 C., if it is desired to bring out the Golgi-nets.) After the ammonium molybdate treatment, the tissues are rinsed in distilled water, placed in 96% alcohol for from ten to twenty- four hours, then in absolute alcohol for a like period, cleared in xylol or toluol, and imbedded in paraffin. Sections having a thickness of 10 // are now cut and fixed to slides with Mayer's albumin-glycerin. Since the various solutions used in the fixation and further treatment of the tissues do not act with the same intensity on all parts of the piece of tissue to be studied, and since the differentiation and staining depend on a relative proportion (not yet fully determined) of the mordant (ammonium molybdate) and the stain in a given section, it is advised by Bethe to cut large numbers of sections and fix to each slide about three sections from different parts of the series. After fixation of the sections to the slide the paraffin is removed with xylol ; and they are then carried through absolute alcohol into distilled water, in which, however, the sections remain only long enough to re
444 THE CENTRAL NERVOUS SYSTEM.
move the alcohol. The slides (with the sections fixed to them) are then taken from the water and rinsed with distilled water from a water-bottle. The slide is then wiped dry on its under surface and edges with a clean cloth, and about i c.c. to 1.5 c.c. of distilled water placed on the slide over the sections. The slides are now placed in a warm oven with a temperature of 55 C. to 60 C. for a period of time varying from two to ten minutes. No definite time can here be given ; sections from each block of tissue need to be tested until the right stay in the warm oven is ascertained. The slides are then taken from the warm oven and rinsed two or three times in distilled water and again dried as previously directed. They are then covered with the following staining solution and again placed in the warm oven for about ten minutes : toluidin-blue, i part ; distilled water, 3000 parts. The stain is washed off with distilled water and the sections are placed in 96% alcohol until no more stain is given off usually for from three-fourths to two minutes. They are then dehydrated in absolute alcohol, passed through xylol twice, and mounted in xylol balsam. For a fuller discussion of this method the reader is referred to Bethe's account in " Zeitsch. f. Wissensch. Mikrosk.," vol. xvn, 1900.
For staining neuroglia Weigert (95) has recommended a method, from which we give the following : A solution is made consisting of 5% neutral acetate of copper, 5% ordinary acetic acid, and 2.5% chrome -alum in water. The chrome-alum and water are first boiled together, the acetic acid then added, and finally the finely pulverized neutral copper acetate, after which the mixture is thoroughly stirred and allowed to cool. To this solution 10% formalin may be added. Objects not over 0.5 cm. in diameter are placed in this fluid for eight days, the mixture being changed at the end of a few days. By this means the pieces of tissue are at the same time fixed and prepared for subsequent staining by the action of the mordant. If separation of the two processes be desired, the specimens are fixed for about four days in a 10% formalin solution (which is changed in a few days), and then placed in the chrome-alum mixture without the addition of formafin. Specimens thus fixed may be preserved for years without disadvantage, and may then be subjected to further treatment by other methods, Golgi's for instance. Washing with water, dehydration in alcohol, and imbedding in celloidin are the next steps. The sections are then placed for about ten minutes in a 0.33% solution of potassium permanganate, washed by pouring water over them, and placed in the reducing fluid (5% chromogen and 5% formic acid of a specific gravity of 1.20; then filter carefully, and add 10 c.c. of a 10% solution of sodium sulphite to 90 c.c. of the fluid). The sections, rendered brown by the potassium permanganate, readily decolorize in a few minutes, but it is better to leave them for from two to four hours in the solution. If it be desirable to decolorize entirely the connective tissue, no further steps need be taken preliminary to staining ; if not, the reducing fluid is poured off and the sections are rinsed twice in water and then placed in an ordinary saturated solution of chromogen (5% chromogen in distilled water, carefully filtered). The sections are left in this solution overnight, and the longer they remain in it, the more marked will be the contrast, as far as stain is concerned, between the connective and nervous tissues ; then water is again twice poured upon the sections and they are ready for staining. This process consists in a
TECHXIC. 445
modified fibrin stain (yid. Technic). The iodo-iodid of potassium solution is the same (saturated solution of iodin in a 5 % iodid of potassium solution). Instead of the customary gentian-violet solution, a hot saturated alcoholic (70% to 80% alcohol) solution of methyl-violet is made, and, after cooling, the clear portion decanted off; to every 100 c.c. of this fluid 5 c.c. of a 5% aqueous solution of oxalic acid is added. The staining takes place in a very short time. The sections are then rinsed and normal salt solution and the iodo-iodid of potassium solution poured over them (5% iodid of potassium solution saturated with iodin), and washed off with water and dried with filter-paper and decolorized in the anilin oil-xylol solution in the proportion of 1:1. The reactions are rapid, and the thickness of the section should not exceed 20 //. This method is best adapted to the central nervous system of the human adult ; it has as yet not been sufficiently tested for other vertebrates.
Mallory' s Selective Neuroglia Fiber-Staining Methods. Fix tissues in io c /c formalin four days ; place in saturated aqueous solution of picric acid four days ; place in 5 f/ c aqueous solution of ammonium bichromate four to six days in warm oven at 38 C.; dehydrate and imbed in celloidin ; sections may be stained in Weigert's fibrin stain and differentiated with equal parts of anilin oil and xylol, or they may be treated as follows: Place sections in 0.5% aqueous solution of permanganate of potassium twenty minutes ; wash in distilled water one to three minutes ; place in i f/ c aqueous solution of oxalic acid thirty minutes ; wash in distilled water ; stain in phosphotungstic-acid-hematoxylin solution (hematoxylin i g., distilled water 8oc.c.,io% aqueous solution of phosphotungstic acid [Merk], 20 c.c., peroxid of hydrogen [U.S. P.], 2 c.c.) for twelve to twenty-four hours ; rinse in distilled water and place for five to twenty minutes in an alcoholic solution of ferric chlorid (ferric chlorid 30 g-> 2>% alcohol 100 c.c.) ; rinse in distilled water and dehydrate quickly, clear in oil of bergamot, and mount in xylol-balsam.
Benda' s Selective Neuroglia Staining Method. Benda has for some years concerned himself with perfecting selective staining methods for differentiating certain constituents of the protoplasm of cells, and has recently published a number of staining methods, by all of which neuroglia fibers may be more or less successfully differentiated. According to him, certain hematoxylin solutions, used after proper fixation and mordanting of the tissues, maybe used for neuroglia stains; also hematoxylin staining, followed by staining with an acid-anilin water crystal violet solution. These will not be considered here. We wish, however, to call especial attention to the following method for staining neuroglia tissue, suggested by Benda, since it has certain advantages not possessed by other selective neuroglia stains. Fix small pieces of tissue in 10% formalin; place in Weigert's chrome-alum solution (formula given above), four days in warm oven at 38 C. ; wash in water twenty-four hours ; dehydrate in graded alcohols ; imbed in paraffin ; cut thin sections and fix these to slides with the albumin -glycerin fixative ; remove paraffin and place sections in mordant consisting of a 4% aqueous solution of ferric alum ; rinse thoroughly in two tap waters and one distilled water ; place in a sodium sulphalizarate solution (add to distilled water a sufficient quantity of a saturated solution of sodium sulphalizarate in 70% alcohol to give it a sulphur-yellow color) twenty-four hours ; rinse in distilled water ; stain for fifteen minutes in a o. i % aqueous solution toluidin blue, which should be heated after
446 THE EYE.
the sections are in the stain until the solution steams ; allow the stain to cool ; rinse in distilled water ; wash in a i C J C aqueous solution of glacial acetic acid for a few seconds or in acid alcohol (six drops of hydrochloric acid ; 70% alcohol looc.c. ) for a few seconds ; dry sections with filterpaper ; dip sections a few times in absolute alcohol ; differentiate in creosote, ten minutes to an hour control now and then under the microscope ; wash in several xylols and mount in xylol -balsam. Neuroglia fibers blue, chromatin of neuroglia cell nuclei a purplish blue, protoplasm of neuroglia cells brownish red to bluish red.
VIII. THE EYE.
A. GENERAL STRUCTURE.
THE organ of vision consists of the eyeball, or bulbus oculi, and the entering optic nerve.
In the eyeball we distinguish three tunics : (i) a dense external coat, the tunica fibrosa or externa, which may be regarded as a continuation of the dura mater, consisting of an anterior transparent structure, called the cornea, and the remaining portion, known as the tunica sclerotica, or, briefly, the sclera ; (2) within the tunica fibrosa a vascular tunic, the tunica vasculosa or media, subdivided into the choroid, ciliary body, and iris ; (3) an inner coat, the tunica interna, which consists of two layers, the inner being the retina ; the outer, the pigment membrane. The latter lines the internal surface of the tunica vasculosa throughout. Within the eyeball are the aqueous humor, the lens, and the vitreous body. The lens is attached to the ciliary body by a special accessory apparatus the zomda ciliaris. These two structures the lens and its fixation apparatus divide the cavity of the eyeball into two principal chambers, the one containing the aqueous humor and the other the vitreous. The former is further subdivided by the iris into an anterior and a posterior chamber. During life the latter is only a narrow capillary cleft.
B. DEVELOPMENT OF THE EYE,
In man the eyes begin to develop during the fourth week of embryonic life, and at first consist of a pair of ventrolateral diverticula, projecting from the anterior brain vesicle. These evaginations gradually push outward toward the ectoderm, and are then known as the primary optic vesicles. The slender commissural segments connecting the vesicles with the developing brain are termed the optic stalks.
Very soon a process of invagination takes place ; that portion of the vesicular wall nearest the ectoderm is pushed inward, thus
DEVELOPMENT OF THE EYE.
447
forming a double-walled cup the secondary optic vesicle, or optic cup. An internal and an external wall may now be differentiated, continuous at the margin of the cup. At the same time a disc-like thickening of the adjacent ectoderm sinks inward toward the mouth of the cup-shaped optic vesicle, forming the first trace of the lens. During the development of the secondary optic vesicle a groove
Blood-vessels Sphincter
Vein. Canal of Petit, of the iris. Cornea, pupillae. Iris.
Fontana's spaces.
Pigment
layer.
Physiologic excavation.
Macula lutea.
Fig. 35 2 . Schematic diagram of the eye (after Leber and Flemming) : a, Vena vorticosa ; b, choroid ; /, lens.
is formed on its ventral side, extending from the marginal ring into the optic stalk. This is the embryonic optic fissure, or the choroidal fissure. At the edges of the groove the two layers of the optic cup are continuous. This groove serves for the penetration of mesoblastic tissue and blood-vessels into the interior of the optic cup, and in its wall the fibers of the optic nerve develop.
The outer layer of the secondary optic vesicle becomes the pigment membrane ; the inner, the retina. The optic nerve-fibers consist not only of the centripetal neuraxes of certain ganglion cells in the retina, but also of centrifugal neuraxes, which pass out from the brain (Froriep).
The invaginating ectoderm which later constitutes the lens is constricted off from the remaining ectoderm in the shape of a vesi
448 THE EYE.
cle, the mesial half of which forms the lens fibers by a longitudinal growth of its cells, while the lateral portion forms the thin anterior epithelial capsule of the lens. The epithelium of the ectoderm external to the lens differentiates later into the external epithelium of the cornea and conjunctiva, neither of which structures is at this stage sharply defined from the remaining ectoderm. It is only during the development of the eyelids that a distinct demarcation is established. All the remaining portions of the eye, as the vitreous body, the vascular tunic with the iris, the sclera with the substantia propria of the cornea and the cells of Descemet's layer, are products of the mesoderm.
C TUNICA FIBROSA OCULL
J. THE SCLERA.
The sclera is the dense fibrous tissue covering of the eyeball, and is directly continuous with the transparent cornea. At the posterior mesial portion of the eyeball, the sclera is perforated for the entrance of the optic nerve, this region being known as the lamina cribrosa. The sclera consists of bundles of connective-tissue fibers arranged in equatorial and meridional layers. At the external scleral sulcus, in the vicinity of the cornea, the arrangement of the fibers is principally equatorial. The tendons of the ocular muscles are continuous with the scleral fibers in such a manner that those of the straight muscles fuse with the meridional fibers, while those of the oblique muscles are continuous with the equatorial fibers. In the sclera are many lymph-channels communicating with those of the cornea. They are much coarser and more irregularly arranged than those of the cornea, and in this respect simulate the lymphchannels found in aponeuroses. Pigmentation is constantly present at the corneal margin, in the vicinity of the optic nerve entrance, and also on the surface next the choroid. The innermost pigment layer of the sclera is lined by a layer of flattened endothelial cells, and is regarded by some as a separate membrane, known as the lamina fusca ; generally, however, it is regarded as forming a part of the outermost layer of the choroid (lamina suprachoroidea). The external surface of the sclera also presents a layer of flattened endothelial cells, belonging to the capsule of Tenon. Anteriorly, the mobile scleral conjunctiva is attached to the sclera by a loose connective tissue containing elastic fibers.
The cornea is inserted into the sclera very much as a watchcrystal is fitted into its frame. At the sclerocorneal junction is found an annular venous sinus, the canal of Schlemm, which may appear as a single canal or as several canals separated by incomplete fibrous septa. Anteriorly and externally this canal is bounded by the cornea and sclera ; internally, it is partly bounded by the origin of the ciliary muscle. The sclera comprises, therefore, one
TUNICA FIBROSA OCULI.
449
half of the canal-wall, and presents a corresponding circular sulcus, the so-called inner scleral sulcus.
The blood-vessels of the sclera are derived from the anterior and posterior ciliary vessels. The capillaries enter either into the ciliary veins or into the venae vorticosae. The numerous remaining vessels traverse the sclera, extending to the choroid, iris, or scleral margin. At the corneal margin the capillaries form loops.
Cornea!
epithelium.
Basal cells.
Anterior elastic membrane.
Substantia propria.
2. THE CORNEA.
The cornea is made up of the following layers : (i) the anterior or corneal epithelium ; (2) the anterior elastic membrane, or Bowman's membrane ; (3) the ground-substance of the cornea, or substantia propria ; (4) Descemet's membrane; (5) the endothelium of Descemet's membrane.
At the center of the human cornea the epithelium consists of from six to eight layers of cells, being somewhat thicker near the corneal margin. Its basilar surface is smooth and there are no connective-tissue papillae. The basal epithelial layer is composed of cylindric cells of irregular height ; the following layers contain irregular polygonal cells, Fig. 353. Section through the anterior portion while the two or three most of human cornea > X 5o.
superficial layers consist of
flattened cells. The cells of the corneal epithelium are all provided with short prickles, which are, however, very difficult to demonstrate, and between are found lymph-canaliculi. The lower surfaces of the basal cells also possess short processes which penetrate into the anterior basement membrane.
In man the anterior elastic or Bowman's membrane is quite thick, measuring from 6 to 8 tj. in thickness and is apparently homogeneous, but may be separated into fibrils by means of certain reagents. In structure it belongs neither to the elastic nor to the white fibrous type of connective tissue, and may be regarded as a basement membrane. Numerous nerve-fibers penetrate its pores to enter the epithelium. The thickness of this membrane decreases toward the sclera, and it finally disappears about I mm. from the latter.
The substantia propria consists of connective-tissue fibrils grouped into bundles and lamellae. Chemically they do not differ 29
450
THE EYE.
from true connective-tissue fibers (Morochowetz), but are doubly refracting, although the cornea as a whole yields chondrin and not glutin on boiling. There are about sixty lamellae in the human cornea. The fibrils composing each lamella are cemented together and run parallel to one another as well as to the surface of the cornea, but they are so arranged that the fibrils of each lamella cross those of the immediately preceding one at an angle of about twelve degrees. The lamellae themselves are likewise closely cemented to one another. The most superficial lamella, lying immediately beneath the anterior elastic membrane, is composed of finer fibers, the course of which is oblique to the surface of the cornea. Between the anterior and posterior elastic membranes are bundles of fibers, which perforate the various lamellae of the cornea and are consequently known as the perforating or arcuate fibers. Between the lamellae are peculiar, flattened cells, possessing
Lymph-canaliculi.
Corneal space.
Fig. 354. Corneal spaces of a dog ; X 640.
irregular or lamella-like processes, the fixed corneal corpuscles ; these lie in special cavities in the ground substance of the substantia propria, which are known as corneal spaces. In these spaces there are also found a varying number of leucocytes. By means of various methods (silver nitrate and gold chlorid treatment), these corneal spaces may be shown to be part of a complicated lymphatic system, comparable to the lymph-canalicular system of fibrous connective tissue. This system of canals is also in communication with the lymph-channels at the corneal margin.
The posterior elastic or Descemet's membrane is not so intimately connected with the substantia propria as Bowman's membrane. It is thinnest at the center of the cornea, and becomes thicker toward the margin. It may be separated into finer lamellae, is very elastic, resists acids and alkalies, but is digested by trypsin.
TUNICA FIBROSA OCULI. 451
At the periphery that is, at the edge of the cornea Descemet's membrane goes over into the fibers of the ligamentum pectinatum.
The endothelium of Descemet's membrane consists of low, quite regular hexagonal cells, which in certain vertebrates (dove, duck, rabbit) are peculiar in that a fibrillar structure may be seen in that portion of each cell nearest the posterior elastic membrane. By means of these fibers, not only adjacent cells, but also those further apart, are joined together. Thus we have here to a marked degree the formation of fibers which penetrate the cells and connect them with one another, conditions already met with in the prickle-cells of the epidermis.
The cornea is nonvascular. In fetal life, however, the capillaries from the anterior ciliary arteries form a precorneal vascular network immediately beneath the epithelium, a structure which is obliterated shortly before birth and only rarely seen in the newborn. Its remains are found at the corneal limbus either as an episcleral or conjunctival network of marginal capillary loops. Fine branches of the anterior ciliary arteries extend superficially along the sclera to the corneal margin, and form here a network of capillaries also ending in loops, from which numerous veins arise, constituting a corresponding network emptying into the anterior ciliary veins. The conjunctival vessels likewise form a network of marginal loops at the corneal limbus, and are connected with the episcleral vessels (Leber). Under pathologic conditions the cornea may become vascularized from the marginal episcleral network.
The nerves of the cornea are derived from the sensory fibers of the ciliary nerves, which form a plexus at the corneal margin ; from this, nonmedullated fibers penetrate the cornea itself and form two plexuses, a superficial and a ground plexus ; the latter is distributed throughout the whole substantia propria with the exception of its inner third (Ranvier, 81). The two plexuses are connected by numerous anastomoses. At one time it was supposed that direct communication existed between the corneal corpuscles and the nervefibers of both plexuses. This view, however, contradicts the generally accepted neurone theory.
Nerve-fibers from the superficial plexus pass through the anterior, elastic membrane and form a plexus over the posterior surface of the epithelium, known as the subcpithelial plexus. From the latter nerve-fibers extend between the epithelial cells, terminating in telodendria with long slender nerve-fibrils, which end in small nodules. Many of the fibrils reach almost to the surface of the epithelium (Rollet, 71 ; Ranvier, 81 ; Dogiel, 90).
Smirnow (1900) has described a rich nerve -supply for the sclera, consisting of both medullated sensory fibers and nonmedullated sympathetic fibers, derived mainly from the ciliary nerves. The sympathetic fibers supply the blood-vessels; the sensory fibers terminate in free endings between the connective-tissue lamellae.
452
THE EYE.
D. THE VASCULAR TUNIC OF THE EYE.
THE CHOROID, THE CILIARY BODY, AND THE IRIS.
From without inward the following layers may be differentiated in the choroid : (i) the lamina suprachoroidea ; (2) the lamina vasculosa Halleri ; (3) the lamina choriocapillaris ; and (4) the glassy layer, or vitreous membrane.
The lamina suprachoroidea consists of a number of loosely arranged, branching and anastomosing bundles and lamellae of fibrous tissue, joined directly to the sclera. These bundles and lamellae consist of white fibrous connective tissue containing numerous elastic fibers, among which a few connective-tissue cells are distributed. Pigment cells are also present in varying numbers. The bundles and lamellae are covered by endothelial cells, and the spaces and clefts between them, and between the lamina suprachoroidea and the lamina fusca, constitute a system of lymph-channels the peric /toroidal lymph-spaces.
Sclera.
Lamina supra choroidea.
Lamina vascu- __, losa Halleri.
Lamina choriocapillaris. Glassy layer. -UaSa
Fig. 355. Section through the human choroid ; X I 3 The lamina vasculosa of the choroid is also composed of similar lamellae, which, however, are more closely arranged. The bloodvessels constitute the principal portion of this layer, the vessels being of considerable caliber, not capillaries. They are so distributed that the larger vessels, the veins, occupy the outer layer of the lamina vasculosa. The venous vessels converge toward four points of the eyeball, forming at the center of each quadrant one of the four vence vorticosa. The arteries, on the other hand, describe a more meridional course.
THE VASCULAR TUNIC OF THE EYE. 453
In the inner portion of this layer is found a narrow zone, in the human eye only about 10 fj. in thickness, consisting largely of elastic fibers and free from pigment cells, known as the boundary zone. This zone is somewhat thicker in many mammals, and in some of these presents a characteristic structure. In the eyes of ruminants and horses this zone consists of several layers of connective-tissue bundles, and is known as the tapetwn fibrositm. It gives the peculiar luster often seen in the eyes of these animals. In the eyes of carnivora this zone consists of several layers of endothelioid cells, containing in their protoplasm numerous small crystals and forming the iridescent layer known as the tapetum cellulosinn.
The lamina choriocapillaris contains no pigment and consists principally of capillary vessels, which form an especially dense network in the neighborhood of the macula lutea. As the venous capillaries become confluent and form smaller veins, the latter arrange themselves in long, radially directed networks, and form in this way the more or less pronounced stellulce vasculosce (Winslowii).
The vitreous or glassy membrane is a very thin (2 /*) homogeneous membrane which shows on its outer surface the impressions of the vessels composing the lamina choriocapillaris, and on its inner surface those of the pigment epithelium of the retina.
At the ora serrata the choroid changes in character ; from this region forward, the choroidal tissue assumes more the appearance of ordinary connective tissue, and the choriocapillary layer is wanting.
The region of the vascular coat extending from the ora serrata to the base of the iris is known as the ciliary body. Its posterior portion, about 4 mm. broad, the orbiculus ciliaris, is slightly thicker than the choroid, and presents on its inner surface numerous small folds, meridionally placed, consisting of connective tissue and bloodvessels. Anterior to the orbiculus ciliaris the ciliary body is thickened by a development of nonstriated muscle the ciliary muscle (see below) ; and on the inner surface of this annular thickening are placed about seventy triangular folds, meridionally arranged the ciliary processes. The attached border of these processes measures from 2 to 3 mm. The anterior border attains a height of about I mm. On and between these folds are found numerous small secondary folds or processes of irregular shape. The ciliary processes consist of fibrous connective tissue and numerous smaller and larger vessels, which have in the main a meridional arrangement. The vitreous membrane extends over the ciliary body, attaining in the region of the ciliary processes a thickness of 3 /J. or 4 fj.. Internal to the vitreous membrane, the ciliary body is covered by a double layer of epithelial cells, the continuation forward of the retina {pars ciliaris retince). Of these, the outer layer is composed of cells, which are deeply pigmented, and are of cubic or short columnar shape, and derived from the outer layer of the secondary optic vesicle, while the cells of the inner layer are nonpigmented and of columnar shape, and are developed from the inner layer of the secondary optic vesicle. In the region of the ciliary processes
454
THE EYE.
their epithelial lining presents here and there evaginations of glandular appearance, lined by the unpigmented cells. These evaginations are known as ciliary glands, and to them is attributed in part, at least the secretion of the fluid found in the anterior chamber of the eye ; it is, however, still a question as to whether these structures are to be regarded as true glands or simply as depressions or crypts in the epithelium.
The ciliary muscle is bounded anteriorly (toward the anterior chamber) by the ligamentum pectinatum iridis, externally by the cornea and sclera, posteriorly by the orbiculus ciliaris, and internally by the ciliary processes. It consists of nonstriated musclefibers in the majority of vertebrates. This muscle is divided into three portions. The outer or meridional division extends from the posterior elastic lamina of the cornea and its continuation, forming the inner wall of the sinus venosus sclerae, to the posterior portion of the ciliary ring. The origin of the middle division is identical with
Cornea! epithelium.
Substantia propria.
Descemet's
membrane. Canal of Schlemm.
Iris. .-.. Pigment layer.
Loose connective tissue of the conjunctiva.
Conjunctiva.
Meridional fibers.
Radial fibers.
Miiller's fibers.
Sclera.
Processus ciliares.
Fig. 356. Meridional section of the human ciliary body ; X 2O that of the outer, but its fibers (assuming that we have before us a meridional section) spread out like a fan, and occupy a large area at their insertion into the ciliary ring and ciliary processes. The radial course of these fibers is mterrupted by circular bundles. The third or inner division {fibrce circulares, fibers of Mutter} is situated between the ligamentum pectinatum, the ciliary processes, and the middle portion of the muscle just mentioned, and is thus near the base of the iris.
Between the ciliary muscle and the posterior elastic membrane of the cornea is an intermediate, richly cellular tissue, which maybe regarded as a continuation of this elastic membrane, and which forms a part of the wall of the sinus venosus. Another structure internal to the foregoing and directed posteriorly is foe.' ligamentum pectinatum iridis, which encircles the anterior chamber and is a continuation of Descemet's membrane to the base of the iris. It con
THE VASCULAR TUNIC OF THE EYE. 455
sists of fibers and lamellae lined by endothelial cells, and bounds certain intercommunicating spaces lying in the ligament, known as the spaces of Fontana. The latter communicate on the one side with the perivascular spaces of the sinus venosus sclerae (canal of Schlemm), and on the other with the anterior chamber.
The iris must be looked upon as a continuation of the choroid, and is connected at its anterior peripheral portion with the ligamentum pectinatum. The iris possesses the following layers, beginning anteriorly : (i) the anterior endothelium; (2) the ground layer, or stroma of iris, together with the sphincter muscle of the pupil ; and (3) the two-layered, pigmented epithelium the pars iridica retinae, of which the anterior is in part replaced by a peculiar muscle tissue, developed from the ectoderm and forming the dilator of the pupil.
The anterior endothelium is a single layer of irregularly polygonal, nonpigmented cells, and is directly continuous with the endothelium of the pectinate ligament.
The ground-layer or stroma of iris consists anteriorly of a fine reticulate tissue rich in cellular elements (reticulate layer). The remaining strata which form the bulk of the ground-layer constitute its vascular layer. The vessels are here peculiar in that they are covered by coarse, circular, connective -tissue fibers forming vascular sheaths. There is also an entire absence of muscular tissue in the vessel walls. The nerves, too, are enveloped by a dense connective tissue. In all eyes (except the albinotic) pigment is found in the connective tissue.
On the posterior inner surface of the ground-layer is a band of smooth muscle-fibers encircling the pupil the sphincter muscle of the pupil. Posterior to this and in intimate relation with the layer of pigmented epithelium covering the posterior surface of the iris is a layer of spindle-shaped cells having a radial arrangement and containing pigment. Closer microscopic inspection reveals the fact that in all probability these elements represent muscular tissue. Here, therefore, we have to deal with a dilator muscle of the pupil. There has been much discussion as to the existence and structure of this muscle. Recent investigations (Szili) indicate that it is developed from the outer layer of the secondary optic vesicle.
The posterior epithelium is the direct continuation of the two epithelial layers of the ciliary body, and represents the anterior portion of the secondary optic vesicle, the two layers being continuous at the margin of the pupil. In the iris both layers of cells, so far as they exist, are pigmented.
The arteries of the choroid are derived from the short posterior ciliary, the long ciliary, and the anterior ciliary arteries. The short posterior ciliary arteries penetrate the sclera in the vicinity of the optic nerve, where they anastomose with branches from the retinal vessels, and spread through the choroid, where they form the choriocapillary layer. The long posterior ciliary arteries (a mesial and a lateral) penetrate the sclera and course forward between choroid and sclera to the ciliary body, forming there the circulus arteriosus iridis major; they
456
THE EYE.
also supply the ciliary muscle, the ciliary processes, and the iris, and anastomose in the ciliary ring with the branches of the short posterior and anterior ciliary arteries. The latter lie beside and partly within the straight ocular muscles, penetrating the latter at the anterior margin of the sclera ; they give off branches to the circulus arteriosus iridis major and to the ciliary muscles, anastomosing at the same time with the posterior ciliary arteries. (Compare Figs. 352 and 357.) Within the iris the blood-vessels generally take a radial direction, but also anastomose with one another, forming capillaries, and subsequently the circulus arteriosus iridis minor at the inner pupillary margin. From the region supplied by the posterior ciliary arteries most of the blood is carried toward the vorticose veins. The anterior ciliary veins convey the blood coming from the arteries of the same name. Into these veins is also poured the blood from the veins lying in the canal of Schlemm, the canal itself being in reality an open venous sinus. Besides this, these veins convey also venous blood from the conjunctiva (Leber). The nonstriated muscle of the ciliary body and iris receives its innervation through sympathetic nerve-fibers, neuraxes of sympathetic neurones, the cell- bodies of which are situated either in the ciliary ganglia or in the superior cervical ganglia. The neuraxes of the sympathetic cells forming the ciliary ganglia form the short
ciliary nerves, which pierce the sclera in the neighborhood of the optic nerve and pass forward, to terminate in the muscle of the ciliary body and the sphincter muscle of the pupil. Stimulation of these nerves causes a contraction of the ciliary muscle and a closure of the pupil'. The cell-bodies of the sympathetic neurones forming the ciliary ganglia are surrounded by pericellular plexuses, the terminations of small medullated nerve -fibers (white rami fibers) which reach the ciliary ganglia through the oculomotor nerves. Neuraxes of sympathetic neurones, the cell-bodies of which are situated in the superior cervical ganglia, reach the eye through the cavernous plexuses, to terminate, it is thought, in part, at least, in the dilator of the iris, since stimulation of these nerves causes a dilatation of the
Margin of pupil.
Choroid.
Fig. 357. Injected blood-vessels of the human choroid and iris ; X 7
THE INTERNAL OR NERVOUS TUNIC OF THE EVE. 457
pupils. The cell-bodies of these sympathetic neurones are surrounded by pericellular plexuses, the terminations of white rami fibers which leave the spinal cord through the first, second, and third thoracic nerves (Langley), and which reach the superior cervical ganglia through the cervical sympathetic.
Melkirch and Agababow have shown that numerous sensory nerves terminate in free sensory endings in the connective tissue of the ciliary body and iris. The sensory nerve-supply of the iris is especially rich.
E. THE INTERNAL OR NERVOUS TUNIC OF THE EYE.
This tunic is composed of two layers : the outer, or stratum pigmenti ; and the inner, or retina.
\. THE PIGMENT LAYER.
The pigment layer develops, as we have seen, from the outer layer of the secondary optic vesicle. It consists of regular hexagonal cells, 12 fj. to 1 8 ii in length and 9 // in breadth, which contain black pigment in the form of granules. The inner surfaces of these cells possess long, thread-like and fringe-like processes, between which project the external segments of the rods and cones of the retina, yet to be described. The nuclei of the pigment cells lie in the outer ends of the cells, the so-called basal plates, and are not pigmented. The distribution of the pigment varies according to the illumination of the retina. If the latter be darkened, the pigment collects at the outer portion of each cell ; if illuminated, the pigment is evenly distributed throughout the whole cell. The pigment granules are therefore mobile (Kiihne, 79).
2. THE RETINA.
The retina has not the same structure throughout. In certain areas peculiarities are noticeable which must be described in detail ; such areas are : (i) the macula lutea ; (2) the region of the papilla (papilla nervi optici) ; (3) the ora serrata ; (4) the pars ciliaris retinae ; and (5) the pars iridica retinae.
We shall begin with the consideration of that portion of the retina lying between the ora serrata and the optic papilla (exclusive of the macula lutea).
From without inward, we differentiate: (i) the layer of visual cells, including the outer nuclear layer ; (2) the outer molecular (plexiform) layer ; (3) the inner nuclear or granular layer ; (4) the inner molecular (plexiform) layer ; (5) the ganglion-cell layer ; (6) the nerve-fiber layer. Besides these, we must also consider the
458
THE EYE.
supporting tissue of the retina and Miiller's fibers, together with the internal and external limiting membranes.
The visual cells are either rod-visual cells or cone-visual cells. The rod-visual cells consist of a rod and a rod-fiber with its nucleus. The rod (40 // to 50 // in length) consists of two segments, an outer and an inner, the former of which is doubly refractive and may be separated into numerous transverse discs by the action of certain reagents. The inner is less transparent than the outer segment, and its inner end shows a fine superficial longitudinal striation due to impressions from the fiber-baskets formed by Miiller's fibers. In the lower classes of vertebrates a rod-ellipsoid
Layer of nerve- '
fibers.
Ganglion-cell layer.
Inner molecular .,
layer.
Inner nuclear layer. i
Outer molecular layer.
Outer nuclear layer.
Ext. limiting membrane. Inner segment of
rod.
Inner segment of cone.
Outer segment of
cone. Outer segment of
rod.
Fig. 358. Section of the human retina ; X 7 (a fibrillar structure) may easily be demonstrated in the outer region of each inner portion ; in many mammalia and in man the demonstration of this is more difficult. This structure is a planoconvex, longitudinally striated body, the plane surface of which is coincident with the external surface of the inner segment, its inner convex surface lying at the junction of the outer and middle thirds of the inner segment. The rod-fibers extend as far as the outer molecular layer of the retina, where they end in small spheric swellings. The nuclei of the rod-visual cells are found at varying points within the rodfibers, but rarely close to the inner segment. When treated with certain fixing agents and stains, the rod-nuclei of certain animals (cat and rabbit) are seen to show several zones, which stain alternately
THE INTERNAL OR NERVOUS TUNIC OF THE EYE. 45Q
light and dark (striation of the rod-nuclei). This striation is not gen erally observed in the rod-nuclei of the human retina.
The cone-visual cells consist, similarly to the rod-visual cells, of a cone and a cone-fiber with its nucleus. The cone (15 fi to 25 fJL in length) is, as a whole, shorter than the rod, and its inner segment is considerably broader than that of the rod. The cone ellipsoid comprises the outer two-thirds of the inner segment, and the outer segment has a more conical shape. The cone-fiber likewise extends as far as the outer molecular layer, where it ends in a branched basal plate. Its somewhat larger nucleus is always found in the vicinity of the inner segment of the cone. The inner surfaces of the inner segments, not only of the cone-cells, but also of the rod-visual cells, lie in one plane, corresponding to the external limiting membrane, a structure composed of the sustentacular fibers of Miiller. The rod-fibers and cone-fibers, with the nuclei of the rod- and cone-visual cells, lie between the external limiting membrane and the outer molecular layer. It will be observed, therefore, that the visual cells include the layer of rods and cones and the outer nuclear layer.
The outer molecular layer consists : (i) of the ramifications of Miiller's fibers ; (2) of the knob and tuft-like endings of the visual cells ; and (3) of the dendritic processes of the bipolar cells of the inner nuclear layer. These structures will be considered more in detail in discussing the relations of the elements comprising the retina.
The inner nuclear layer contains: (i) the nucleated stratum of Miiller's sustentacular fibers ; (2) ganglion cells situated in the outer region of the layer and extending in a horizontal direction ; (3) bipolar ganglion cells with oval nuclei, densely placed at various depths of the layer and vertical to it ; (4) amacrine cells (neurones, apparently without neuraxes) lying close to the inner margin of the layer and forming with their larger nuclei a nearly continuous layer of so-called spongioblasts. The numerous processes of these spongioblasts lie in the inner molecular layer, the composition of which will be further discussed later.
The ganglion-cell layer of the optic nerve consists, aside from centrifugal neuraxes and the fibers of Miiller, which are here present, of multipolar ganglion cells, the dendrites of which extend outward and the neuraxes of which are directed toward the optic nerve-fiber layer. These cells vary in size, and their nuclei are typical, being relatively large, deficient in chromatin, and always provided with large, distinct nucleoli. In man the optic nervefibers of the retina are nonmedullated.
All these structures are typical of that portion of the retina lying behind the ora serrata. The retina in the vicinity of the optic papilla and macula lutea must be taken up separately.
460
THE EYE.
3. REGION OF THE OPTIC PAPILLA.
The optic papilla is the point of entrance of the optic nerve into the retina. At the center of the papilla, in the region where the nerve-fibers spread out radially in order to supply the various areas of the retina, is a small, funnel-shaped depression, the physiologic excavation. The fibers of the optic nerve lose their medullary sheaths during their passage through the sclera and choroid, and then continue to the inner surface of the retina, over which they spread in a layer which gradually becomes thinner toward the ora serrata. On account of the deflection of the nerve- fibers, and because, during
Physiologic excavation.
Layer of nerve-fibers....
Inner nuclear layer. ""
Outer molecular lay, T. Outer nuclear layer.. Rods and cones. '
Pigment layer. .-'
Sclera.
Lamina cribrosa.--'
Fig. 359. Section through point of entrance of human optic nerve ; X 4
their passage through the sclera, they lose their medullary sheaths
at one and the same point, the optic nerve becomes suddenly
thinner. The result is a deeply indented circular depression in this
region. On this depression border the three ocular tunics. At this
point the retina is interrupted, the outer layers extending to the bottom of the depression, while the inner cease at its margin. In many
cases the outer layers of the retina are separated from the optic nerve
by a thin lamina of supporting tissue (intermediate tissue).
4. REGION OF THE MACULA LUTEA.
At the center of the macula lutea is a trough-like depression, the fovea centralis, the deepest part of which, \hzfnndits, lies very close to the visual axis. Here the layers of the retina are practically reduced to the cone-visual cells. The margin of this depression is somewhat thickened, owing to an increase in the thickness of the nerve-fiber and ganglion-cell layers. Toward the fundus of the fovea each of the four inner retinal layers becomes reduced in thickness, the inner layer first and the three others in their order : the inner molecular layer, however, seems to extend as far as the fundus. As we have seen, only the cone-visual cells are found in the fovea centralis, there being an entire absence of the rod-visual cells. Since the nuclei of the cone -visual cells are in the immediate neighborhood
THE INTERNAL OR NERVOUS TUNIC OF THE EYE. 461
of the cones, and since the cone-fibers, in order to reach the outer molecular layer, must here describe a curve, there arises a peculiar 1 ayer, composed of obliquely directed fibers, known as the outer fiber-layer or Henle's fiber layer. In other words, the fibers of this region are more distinctly seen because they are not covered by the rod-nuclei and rod-fibers.
Fovea centralis. Layer of "TSHW9^BO!ftfc^ i
nerve-fibers. ! QGanglion-cell . ?' ~^
layer.
Inner molecu- L "
lar layer. Inner nuclear .
layer. Outer molec-..^
ular layer. -" ><
Outer fibrous g
layer.
Outer nuclear -4H layer.
Cones. ... I
Fig. 360. Section through human macula lutea and fovea centralis ; X 1 S- As a result of treatment with certain reagents, the fovea centralis is deeper and the margin more precipitous than during life.
The yellowish color of the fovea centralis is due to pigment held in solution within the layers of' the retina. The cone-visual cells themselves contain no pigment.
5. ORA SERRATA, PARS CILIARIS RETINAE, AND PARS IRIDICA
RETINAE.
In the region of the ora serrata the retina suddenly becomes thinner. As seen from the inner surface of the retina, its decrease presents the appearance of an irregular curve rather than of the segment of a sphere. Shortly before the retina terminates, its layers become markedly reduced, certain ones disappearing entirely ; first the nerve-fiber layer, then the ganglion-cell layer and cone- and rodvisual cells, their place being taken by an indifferent epithelium. The inner molecular layer of the retina gradually loses the processes which penetrate inward. In the region of the ora serrata the sustentacular fibers are markedly developed. Relatively large hollow spaces are often found in the retina at the ora serrata ; they are thought to be due to edema.
The pars ciliaris retinae consists essentially of two simple layers of cells, of which the external represents the pigment layer and the internal the inner epithelium of the secondary optic vesicle. In the pars iridica retinae the arrangement is similar ; here both layers are pigmented.
462 THE EYE.
6. MULLER'S FIBERS OF THE RETINA.
Genetically, the sustentacular fibers, or fibers of Miiller, in the retina are, like the whole retina, of ectodermic origin, and represent a highly developed form of neurogliar tissue. They penetrate the retina from within and extend as far as the inner segments of the rods and cones. Each fiber represents a long, greatly modified epithelial cell, terminating in one or more broad basal plates, which come in contact with those of adjacent fibers, thus forming a sort of membrane the internal limiting membrane. Owing to its marked plasticity, each fiber presents certain peculiarities within the various layers of the retina through which it penetrates. Thus, within the molecular layers the fiber is provided with transversely directed processes and platelets. Within the nuclear layers, on .the other hand, are numerous lateral indentations, which correspond to the impressions produced by the cells of these layers. At the inner surface of the cones and rods the fibers terminate in endplates, which represent cuticular formations, and, blending with one another, form a single membrane the external limiting membrane. This membrane is perforated by the rod-fibers and cone-fibers. The end-plates of the fibers give off externally short, inflexible fibrils, which form the fiber-baskets containing the basilar portions of the inner segments of the rods and cones. (Via. Fig. 361.) Miiller's fibers do not appear as fibers in chrome-silver preparations, but as complicated cellular structures, as above depicted. In preparations of the retina, stained in a differential neuroglia stain (Benda's method), clearly defined fibers, stained after the manner of neuroglia fibers, may be differentiated. These fibers are in contact with or are imbedded in the protoplasm of the Miiller's fibers.
7. THE RELATIONS OF THE ELEMENTS OF THE RETINA TO
ONE ANOTHER.
We shall now take up the relationships existing between the various elements of the retinal strata, giving the theories now generally accepted and based on observations made with the Golgi and methylene-blue methods, and more particularly on the investigations of Ramon y Cajal (see diagram, Fig. 361) :
1. The inner processes of the rod-visual cells end, as a rule, in small expansions within the outer molecular layer, in which also the processes of the cone-visual cells terminate in broader branched pedicles. In this layer also are situated the terminal arborizations of the dendrites and neuraxes of certain cells belonging to the inner nuclear layer.
2. The inner nuclear layer consists, as we have seen, (a} of bipolar cells, which constitute the principal portion of this layer, [b] of horizontally placed cells lying immediately beneath the outer molecular layer, and (f) of the layer of spongioblasts situated at the junction
THE INTERNAL OR NERVOUS TUNIC OF THE EYE.
463
of the inner nuclear with the inner molecular layer. The bipolar cells comprise the following : (a) Bipolar cells of the rod-visual cells the dendrites of which intertwine around the basilar portions of the rodvisual cells, and the neu raxes of which end in telodendria in the neighborhood of the cell-bodies of the nerve-cells of the ganglion-cell layer. (/9) Bipolar cells of the cone-visual cells. The dendrites of these cells,
sr
which also end in the outer molecular layer, are there in relation to the basilar processes of the cone-fibers. Their neuraxes come in contact, by means of terminal arborizations, with the dendrites of the ganglion cells of the ganglion-cell layer at varying depths of the inner molecular layer, (j] Besides these, there are also bipolar cells which, as in the case of a and ft. form contact with the rod- and
464 THE EYE.
cone-visual cells, but end on the cell-bodies of the ganglion ceils of the ganglion-cell layer. The horizontal cells send their dendrites into the outer molecular layer, while their neuraxes extend horizontally and give off numerous collaterals to the same layer, ending there in telodendria. These cells are of two varieties: the smaller, indirectly connecting the cone-visual cells with one another by means of their dendrites and neuraxes ; and the larger, more deeply situated cells, connecting in a similar manner the basilar ends of the rodvisual cells. A few cells of the second variety give off one or two dendrites each, which penetrate through the inner nuclear layer into the inner molecular layer.
3. The inner molecular layer. This is composed of five strata. The majority of the spongioblasts (amacrine or parareticular cells) in the inner nuclear layer send their processes upward into the inner molecular layer, in which some end in fine arborizations in the first, others in the second, and still others in the third interstice, separating the strata of the inner molecular layer from one another. Besides these so-called stratum spongioblasts, there are also others in the inner nuclear layer, the diffuse spongioblasts, whose ramifications end simultaneously in several or in all of the strata of the inner molecular layer. Besides the ramifications of the spongioblasts just mentioned, autochthonous cells are also present. These lie in one of the interstices of the molecular layers, their ramifications spreading out in a horizontal direction. Besides all these structures the dendrites of the cells in the ganglion-cell layer also ramify throughout the inner molecular layer.
4. The ganglion - cell layer. The cell-bodies are irregularly oval ; their dendrites extend into the inner molecular layer, and their neuraxes into the nerve-fiber layer. According to the manner of their dendritic termination, the ganglion cells may be divided into three groups : (i) those the dendrites of which extend into but one stratum of the molecular layer ; (2) those the dendrites of which extend into several strata of the molecular layer ; and (3) those the dendrites of which are distributed throughout the entire thickness of the molecular layer. Thus, these three groups are made up of the so-called mono-stratified, poly-stratified, and diffuse cells ; by means of their dendrites they come in contact with one or several of the neuraxes of the bipolar cells of the inner nuclear layer.
5. The nerve-fiber layer of the retina. This layer consists of centripetal neuraxes from the ganglion cells of the ganglion-cell layer, and of centrifugal nerve -fibers ending in various layers of the retina, including the outer molecular layer.
8. THE OPTIC NERVE.
Within the orbit the optic nerve possesses an external sheath, which is an extension of the dura mater and is continuous with the scleral tissue, and an inner sheath, which is a prolongation of the pia
THE INTERNAL OR NERVOUS TUNIC OF THE EYE.
465
mater. Between these two sheaths is a fissure, divided into two smaller clefts by a continuation of the arachnoid. Both these clefts are traversed by connective-tissue trabeculae. The inner cleft communicates with the subarachnoid space ; and the outer narrower cleft, with the subdural space.
The fibers of the optic nerve are medullated, but they possess no neurilemma. They are grouped into small bundles by septa and bands of fibrous tissue penetrating the optic nerve from the inner or pial sheath. Within these bundles the nerves are separated by neuroglia tissue, neuroglia cells and fibers, which further forms a thin sheath about each bundle. In the region of the sclera and choroid the optic nerve-fibers lose their myelin, and the septa of the inner or pial sheath become better developed and relatively more numerous. Connective-tissue fibers from the sclera and choroid also traverse this region of the optic nerve, giving rise to what is known as the lamina cribrosa. At from I y 2 to 2 cm. from the eyeball there enter into the optic nerve laterally and ventrally (according to J. Deyl, mesially) the central artery and vein of the retina, which very soon come to lie within the axis of the nerve. Here they are surrounded by a common connective-tissue sheath which is in direct connection with the pial sheath. The optic nerve-fibers extend through the lamina cribrosa into the retina, where they spread out as the nervefiber layer in the manner previously described.
- Vein.
9. BLOOD-VESSELS OF THE OPTIC NERVE AND RETINA. The blood-vessels of the optic nerve are principally derived from the vessels of the pial sheath. In that portion of the nerve containing the central vessels of the retina the latter anastomose with the pial vessels, so that this portion of the optic nerve is also supplied by the central vessels.
At their entrance through the
/ sclera the short posterior ciliary
arteries form a plexus around the optic nerve, the arterial circle of Zinn, which communicates, on the one hand, with the vessels of the pial sheath, and, on the other, with those of the optic nerve. At the level of the choroid the vessels of the latter communicate by means of capillaries with the central vessels of the optic nerve. The central artery and vein of the retina enter and leave the retina at the optic papilla, 30
-- Artery.
the
Zone surrounding artery free from capillaries.
Fig. 362. Injected blood-vessels of human retina ; surface preparation ;
dividing here, or even within
466 THE EYE.
the nerve itself, into the superior and inferior papillary artery and vein. Both the latter again divide into two branches, the nasal and temporal arteriole and venule, known, according to their positions, as the superior and inferior nasal and temporal artery and vein.
Besides these vessels, two small arteries also arise from the trunk of the central artery itself, and extend to the macula. Two similar vessels extend toward the nasal side as the superior and inferior median branches. Within the retina itself the larger vessels spread out in the nerve-fiber layer, forming there a coarsely meshed capillary network connected by numerous branches with a finer and more closely meshed network lying within the inner
- - Vascular
plexus of
macula lutea
with wide
meshes.
Fovea centra1 is, free from
vessels.
Fig. 363. Injected blood-vessels of human macula lutea ; surface preparation ; X 28.
nuclear layer. The venous capillaries of this network return as small venous branches to the nerve-fiber layer, in which they form a venous plexus, side by side with the arterial plexus.
The arteries of the retina are of smaller caliber than the veins. The larger arteries possess a muscular layer ; the smaller, only an adventitia. All the vessels possess highly developed perivascular sheaths. The visual-cell 'layer is nonvascular, as are also the fovea centralis and the rudimentary retinal layers lying anterior to the ora serrata.
The arteries of the retina anastomose with one another solely by means of capillaries (end-arteries), and it is only in the ora serrata that coarser venous anastomoses exist.
THE CRYSTALLINE LENS. 467
F. THE VITREOUS BODY.
The vitreous body is a tissue which consists almost entirely of fluid, containing very few fixed cellular elements and only a small number of leucocytes, which are found more particularly in its outermost portion. Thin structureless lamellae and fibers occur throughout the entire vitreous body, with the exception of the hyaloid canal. These fibrils form an interlacing network with wide meshes. They differ chemically from both the white fibrous tissue and yellow elastic fibers, resembling in some respects cuticular formations (von Ebner). These are particularly numerous at the periphery and especially in the region of the ciliary body. Toward the surface the fibrils are more densely arranged, forming the hyaloid membrane of the vitreous body, separating the latter from the retina. This membrane is somewhat thicker in the region of its close attachment around the physiologic excavation of the optic nerve and to the internal limiting membrane of the retina in the ciliary region. In the latter region the hyaloid membrane is in close relation with the epithelium of the pars ciliaris retinas. It does not, however, penetrate into and between the ciliary processes, but extends like a bridge over the furrows between them. This arrangement gives rise to spaces, the recessus camera posterioris, which form a division of the posterior chamber, and are inclosed between the hyaloid membrane, the ciliary processes, the suspensory ligament of the lens, and the lens itself; these spaces are filled with aqueous humor. In the region of the ciliary processes the hyaloid membrane is closely associated with numerous fibers, which diverge fan-like toward the lens and become blended with the outer lamella of the lens-capsule. These fibers appear to arise from the epithelium of the pars ciliaris retinas, and may be regarded as cuticular formations. Those coming from the free ends of the ciliary processes become attached along the equator of the lens and to the adjacent posterior portion of the lens-capsule. On the other hand, the fibers originating between the ciliary processes attach themselves to the anterior surface of the lens-capsule in the immediate vicinity of the equator. Together these fibers constitute the zonula ciliaris, zonulc of Zinn, or the suspensory ligament of the lens. Between these fibers of the zonula and the lens itself there is, consequently, a circular canal divided by septa, the canal of Petit, which communicates by openings with the anterior chamber.
G. THE CRYSTALLINE LENS.
As we have already, seen, the crystalline lens originates as an ectodermic invagination, which then frees itself from the remaining ectoderm in the shape of a vesicle and becomes transformed into the finished lens. In this process the cells of the inner wall of the vesicle become the lens-fibers, while those of the outer portion re
468 THE EYE.
main as the anterior epithelium of the lens. The lens is surrounded on all sides by the lens-capsule.
The lens capsule is a homogeneous membrane, nearly twice as thick on the anterior surface of the lens as on the posterior. Its chemic reactions differ from those of connective tissue, and in this respect it may be compared with the membranae propriae of glands. In sections the lens capsule appears to possess a tangential striation ; under the influence of certain reagents, and under proper preliminary treatment, lamellae may be detached from its surface which are found to be directly connected with the fibers of the suspensory ligament.
The anterior epithelium consists, in the fetus, of columnar cells , in children, of cells approaching the cubic type ; and in the adult, of decidedly flattened cells. Toward the equator of the lens, in the so-called transitional zone, the cells increase in height and gradually pass over into the lens fibers.
The lens fibers are also derivatives of epithelial cells ; they are long, flattened, hexagonal prisms, which extend through the entire thickness of the lens. In the adult the lens may be differentiated into a resistant peripheral and a softer axial substance. The surfaces of the fibers present irregularities, and it is with the help of these serrations and a cement substance that the fibers are bound together. Each fiber possesses one or more nuclei, which, although they have no constant position, are usually found in the middle of the fibers situated near the lens-axis, and in the anterior third of those at some distance from the axis. The course of the fibers in the lens is extremely complicated.
R THE FETAL BLOOD-VESSELS OF THE EYE.
In the eye of the embryo the vitreous body and the capsule of the lens contain blood-vessels. The vessel which later becomes the central artery of the retina passes through the space subsequently occupied by the vitreous body as far as the posterior surface of the lens (anterior hyaloid artery) and branches in the region of the posterior and anterior lens-capsule. The anterior vascular membrane of the lens capsule of the embryo is known as the membrana capsulopupillaris, and that portion corresponding to the pupil, as the membrana pupillaris. In the embryo numerous other vessels arise at the papilla and extend over the surface of the vitreous body close to the hyaloid membrane ; these are the posterior Jiyaloid arteries. These vessels later disappear. In place of the anterior hyaloid artery there remains in the vitreous humor a transparent cylindric cord containing no fibers nor lamellae, as is the case in the remaining portion of the vitreous body, and consisting of a more fluid substance ; this is the hyaloid canal, or the canal of Cloquet.
THE PROTECTIVE ORGANS OF THE EYE. 4.69
With regard to the posterior hyaloid vessels, the generally accepted theory is that they later enter into the formation of the retinal vessels. Little is known as to the details of this process ; but the fact remains that, in the rabbit, for instance, the larger branches of the retinal vessels are internal to the inner limiting membrane, and, therefore, within the vitreous body, and that they send smaller branches into the retina (His, 80).
I. INTERCHANGE OF FLUIDS IN THE EYEBALL.
The anterior lymph-channels of the eye comprise (i) the lymph-canaliculi of the cornea, which communicate with similar structures in the sclera ; (2) the system of the anterior chamber, which is indirectly connected, on the one hand, with the canal of Schlemm by means of the spaces of Fontana, and with the stroma iridis, into which the ligamentum pectinatum extends ; while, on the other hand, it communicates with the posterior chamber and its recesses, and with the canal of Petit.
In the posterior region of the eyeball are the lymph-channels of the retina (the perivascular spaces), those of the optic nerve, the space between the pigment layer and the remaining portion of the retina (interlaminar space, Rauber), and the lymph-spaces of the choroid and sclera. The influx and efflux of intraocular fluid occur principally by means of filtration. The influx takes place through the ciliary processes ; that the choroid has to do with this process is very improbable. The efflux takes place through the veins of the canal of Schlemm, into which the fluid filters through the cement lines of the endothelial lining of the canal of Schlemm, finally emptying into the anterior ciliary veins. A posterior efflux from the vitreous body probably does not exist, or at least occurs to a very limited extent. The anterior chamber possesses no efferent lymph-vessels (Leber, 95).
J. THE PROTECTIVE ORGANS OF THE EYE.
J. THE LIDS AND THE CONJUNCTIVA.
At the end of the second month of embryonic life the eyelids begin to develop in the shape of two folds of skin. At the end of the third month these folds come in contact in the region of what is later the palpebral fissure, and grow together at their outer epithelial margins. Shortly before birth the two lids again separate and the definitive palpebral fissure is formed.
The eyelids show three distinct layers : (i) the external cutis, which presents special structures at its free margin and continues about I mm. inward from the inner border of the free margin ; (2) the mucous membrane, or palpebral conjunctiva, beginning from
47 THE EYE.
this line and covering the entire internal surface j and (3) a middle layer.
1 . The cuticular portion of the eyelid consists of a thin epidermis and a dermis poorly supplied with papillae. Fine lanugo-like hairs with small sebaceous glands and a few sweat-glands are distributed over its entire surface. The cutaneous connective tissue is very loose, contains very few elastic fibers, and is supplied with pigment cells in the superficial layers. At the lid-margin the papillae are well developed and the epidermis is somewhat thickened. The anterior margin supports several rows of larger hairs, the cilia, the posterior row of which possesses, besides the sebaceous glands, modified sweat-glands, the ciliary glands of Moll, which also empty into or near the hair follicles. The ciliary glands are readily distinguished from the sweat glands ; their tubules are relatively large, often showing alternating large vesicular segments and short narrow segments. A branching of the tubules has also been observed (Huber). The eyelids are further provided with numerous glands, known as the Meibomian or tarsal glands. About thirty of these glands are found in the upper, a slightly smaller number in the lower, lids. They lie within the tissue of the tarsus vertical to the palpebral margin. Each gland consists of a tubular duct, lined by stratified squamous epithelium, beset with numerous simple or branched alveoli lined by a stratified, cubic epithelium in every respect similar to that lining the alveoli of sebaceous glands. The ducts of these glands terminate at the palpebral margin posterior to the cilia. (See Fig. 364.)
2. The conjunctival portion of the eyelids is lined by a simple pseudostratified columnar epithelium, possessing two strata of nuclei. This is continuous with the bulbar conjunctiva at the conjunctival fornix, and is characterized by the occasional presence of folds and sulci. Longitudinal folds in the upper portion of the upper lid running parallel with the lid-margin are frequently present. Goblet cells are usually found in the epithelium. According to W. Pfitzner (97), the epithelium of the conjunctiva consists of two or three strata of cells, of which the more superficial possess a cuticular margin. Certain structures which have always been regarded as goblet cells are in all probability similar to the cells of Ley dig i. e., mucous cells, which do not pour their secretion out over the surface of the epithelium. Some lymphoid tissue is always found in the stratum proprium of the mucous membrane, and occasionally it is seen to form true lymph-nodules. It is of some interest to note that a marked production of these lymph-nodules occurs in certain diseases. Such lymph-nodules are usually associated with epithelial crypts, which fact led Henle to regard them as glandular formations. Small glands with a structure similar to that of the lacrimal glands are also present in the palpebral conjunctiva ; they are known as accessory lacrimal glands and are found in the upper eyelid, at the outer angle of the conjunctival fornix. Similar glands occur also at the mesial angle of the fornix.
THE PROTECTIVE ORGANS OF THE EYE.
471
3. Besides the tarsus (fibrocartilage) the middle layer of the eyelid contains : (i) The musculus orbicularis oculi, which lies beneath
Fig. 364. Vertical section of the upper eyelid of man; X *4 : af > arterial arcus tarseus ; c, cilia ; dgt, excretory duct of Meihomian gland ; glc, ciliary gland (Moll) ; McR,
ciliary muscle of Riolani ; Mop, m. orbicularis palpebrarum ; Mt, nonstriated muscle-fibers
of the tarsal muscle and tendon of the levator palpebrae superioris ; nlc, lymph-node of
the conjunctiva palpebrse ; T, tarsus (Sobotta, "Atlas and Epitome of Histology.").
the subcutaneous tissue. At the margin of the lid this structure gives off the musculus ciliaris Riolani, which is composed of two
472
THE EYE.
fasciculi separated by the tarsus. (2) The connective tissue between the bundles of the musculus orbicularis oculi. (3) The connective tissue lying behind the latter and the tarsus. In the upper lid the connective tissue mentioned under 2 and 3 is connected with the tendon of the musculus palpebralis superior. The latter is composed of smooth muscle-fibers, and is regarded as a continuation of the middle portion of the striated, voluntary musculus levator palpebrae superioris. The middle layer of the lower lid isstruc
Fig. 365. Meibomian or tarsal gland, reconstructed after Bern's wax-plate method;
X20.
turally analogous, except that here a fibrous expansion from the sheath of the inferior rectus muscle takes the place of the levator palpebrae.
THE PROTECTIVE ORGANS OF THE EYE. 4/3
The blood-vessels of the eyelid lie directly in front of the tarsus, and from this region supply adjacent parts ; they reach the posterior portion of the lid either by penetrating the tarsus or by encircling it (Waldeyer, 74). The lymph-vessels form a plexus in front and one behind the tarsus.
The " third eyelid," the plica semilunaris, contains, when well developed, a small plate of hyaline cartilage.
At the fornix the epithelium of the palpebral conjunctiva becomes continuous with the two- or three-layered squamous epithelium of the conjunctiva bulbi. Beneath this epithelium is found a loose fibre-elastic connective tissue, presenting subepithelial papillae, and quite vascular. In it are found medullated nerve-fibers, some of which terminate in free sensory nerve-endings in theconjunctival epithelium ; others terminate, especially near the corneal margin, in end-bulbs of Krause ; and still others may be traced to the cornea, to terminate in a manner previously described.
2. THE LACRIMAL APPARATUS.
The lacrimal apparatus consists of the lacrimal glands, their excretory ducts, the lacrimal puncta and canaliculi, the lacrimal sac, and the nasal duct.
The lacrimal gland, wnich is a branched tubular gland, is separated into two portions, of which the one lies laterally against the orbit and the other close to the upper lateral portion of the superior conjunctival fornix. The structure of the gland is, on the whole, that of a serous gland (parotid), with the difference that the intralobular ducts are not lined by a striated epithelium such as is found in the salivary tubules, and that those cells which are wedged in between the secretory elements and functionate as sustentacular cells (basketcells) are here much more highly developed.
The excretory ducts of the orbital division generally pass by the conjunctival half of the gland, taking up a few ducts from the latter as they go, and finally empty on the surface of the conjunctiva. Aside from these, the lateral portion of the gland possesses also independent ducts. All the excretory ducts are lined by columnar epithelium and surrounded by a relatively thick connective-tissue wall having inner longitudinal and outer circular fibers. From the lateral portion of the conjunctival culdesac, into which the secretion is brought by the excretory ducts of the lacrimal gland, the secretion passes into the capillary space of the sac, and is then evenly distributed by means of the sulci and papillae over the conjunctival surface of the lid. In this manner the secretion reaches the mesial angle of the lid, whence it passes through the lacrimal puncta into the lacrimal canals.
The nerve supply of the lacrimal glands is from the sympathetic nervous system. The neuraxes of sympathetic neurones accompany the gland ducts and form plexuses about the alveoli, the terminal branches of which may be traced to the gland cells.
474 THE EYE The lacrimal canals are lined by stratified squamous epithelium, and possess a basement membrane as well as a connective-tissue layer containing circularly disposed elastic elements. Externally we find a layer of transversely striated muscle -fibers.
The lacrimal sac is provided with a simple pseudostratified columnar epithelium having two strata of nuclei. In it goblet cells are also found. The nasal duct is lined by a similar epithelium. The connective-tissue wall of the latter and that of the lacrimal sac come in contact with the periosteum ; between them is a welldeveloped vascular plexus. Stratified squamous and ciliated epithelium have been described as being present in the nasal duct, as well as mucous glands in both nasal duct and lacrimal sac. (See works of M. Schultze, 72 ; Schwalbe, 87.)
TECHNIC
The eyes of the larger animals, after having been previously cleaned by removing the muscles and loose connective tissue, are placed in the fixing fluid and cut into two equal parts by means of an equatorial incision. Smaller eyes with thin walls may be fixed whole.
Miiller's fluid, nitric acid, and Flemming's fluid are usually employed as fixing agents. After fixing in one of these fluids, different parts of the eyeball are imbedded in celloidin or celloidin -paraffin and then sectioned.
The corneal epithelium is best macerated in 33% alcohol ; the membrane of Descemet may be impregnated with silver. In order to bring the fibers of the latter into view, Nuel recommends an injection of i jc to 2 f formic acid into the anterior chamber of the eye of a dove or a rabbit, after having drawn off the aqueous humor. The cornea is then cut out, and fixed for from three to five minutes in osmic acid.
The substantia propria is examined either by means of sections or by means of teased preparations from a cornea macerated in limewater or potassium permanganate. The sections are stained with picrocarmin (Ranvier). The corneal spaces and canaliculi may be demonstrated in two ways with the aid of silver nitrate ; either the fresh cornea of a small animal is stripped of its epithelium, cauterized with a solid stick of silver nitrate, and then examined in water, in which case the corneal spaces and their canaliculi show light upon a dark ground (negative impregnation) ; or the corneae of larger animals are treated in the same manner, after which tangential sections are made with a razor, and placed in water for a few days ; in this case the corneal spaces and their canaliculi show dark upon a light ground (positive impregnation, Ranvier, 89).
By means of Altmann's oil method casts of the corneal spaces and their canaliculi may be made. Treatment by the gold method often brings out not only the nerves, but also the corneal corpuscles and their processes.
Ranvier (89) especially recommends a i% solution of the double chlorid of gold and potassium for the corneal nerves. The cornea of the frog is treated for five minutes with lemon-juice, then for a quarter of an hour with i % potassium-gold chlorid solution, and, finally, for one or two days with water weakly acidulated with acetic acid (2
TECHNIC. 475
drops to 30 c.c. of water), the whole process taking place in the light. Golgi's method may also be used, but the gold method is more certain. The sclera is treated in a similar manner.
The pigmentation of the vascular layer interferes with examination, and albinotic animals should therefore be selected ; or the pigment may be removed from the previously fixed eyeball with hydrogen peroxid or nascent chlorin. The latter method is applied exactly as in cases where the removal of osmic acid is desired.
The adult lens is sectioned with difficulty, as it becomes very hard in all fixing fluids. The anterior capsule of the lens may be removed from previously fixed specimens and examined by itself. The lens-fibers are demonstrated by maceration in y^ alcohol (twenty-four hours) or in strong nitric acid. Before immersion the lens-capsule is opened by a puncture.
The retina can rarely be kept unwrinkled in eyes that have been fixed whole. The eyeball should therefore be opened in the fixing fluid and the latter permitted to act internally ; or the external tunics are removed, thereby enabling the fixing fluid to act externally.
Ranvier recommends subjecting the eyes of smaller animals (mouse, triton) for a quarter or half hour to the action of osmic acid fumes (see p. 24), after which the eyes are opened in yi alcohol with the scissors. At the end of three or four hours the posterior half of the eye is stained for some time in picrocarmin (p. 44), then carried over into \ C J C osmic acid for twelve hours, washed with water, treated with alcohol, and cut.
In osmic acid preparations the rod-nuclei show dark transverse bands, a condition due to the fact that the end-regions of the nuclei stain more deeply.
The retina is a good object for differential staining, as, for instance, with hematoxylin-eosin, hematoxylin -orange G, etc. The latter combination is particularly successful in staining the rod- and cone-ellipsoids. The examination of tangential sections should not be omitted.
With the retina the best results are obtained by means of Golgi's method. Attention must be called to the fact that the supporting structures of the retina are more easily impregnated than the nervous elements, and that the latter can be demonstrated to any extent only in very young eyes.
Ramon y Cajal (94) recommends the following method, modified after Golgi : After the removal of the vitreous humor the posterior half of the eyeball is placed for one or two days in a mixture containing 2,% potassium bichromate 20 c.c. and i% osmic acid 5 or 6 c.c. The pieces are then dried with tissue paper and placed in a 0.75% silver nitrate solution for an equal length of time. Without washing, the pieces are immersed for from twenty-four to thirty -six hours in a mixture containing 3% potassium bichromate 20 c.c., and i% osmic acid 2 or 3 c.c., and then again carried over into a 0.75% silver nitrate solution for twenty-four hours. In order to prevent precipitation it is advisable to roll up the retina before treating, and to cover it with a thin layer of a thin celloidin solution, which prevents it from again unrolling.
The methylene-blue method (p. 184) will also bring out the nervous elements of the retina, although the results are not quite so satisfactory as those obtained by Golgi's method.
47" THE ORGAN OF HEARING.
IX. THE ORGAN OF HEARING.
THE ear, the organ of hearing, consists of three parts : (i) The external ear, including the pinna or auricle and the external auditory canal ; (2) the middle ear, tympanum, or tympanic cavity, containing the small ear bones and separated from the external auditory canal by the tympanic membrane, but communicating with the pharynx by means of the Eustachian tube ; (3) the inner ear, or labyrinth, consisting of a bony and a membranous portion, the latter lined by epithelial cells, especially differentiated in certain regions to form a neuro-epithelium, in which the auditory nerves terminate. The first two parts serve for the collection and transmission of the sound-waves ; the complicated labyrinth, with its differentiated neuro-epithelium, for the perception of the same. Figure 366 presents in a schematic way the relationships of the parts here mentioned.
A. THE EXTERNAL EAR.
The cartilage of the ear, including that of the external auditory passage, is of the elastic variety, but differs from typical elastic cartilage in that it contains areas entirely free from elastic fibers. The elastic reticulum is, however, never absent near the perichondrium. The skin covering the pinna is thin, and in it are found hairs with relatively large sebaceous glands ; sweat-glands are found on the outer surface.
The skin lining the cartilaginous portion of the external auditory canal is somewhat mobile and possesses very few. pronounced papillae, and is characterized by the presence of so-called ceruminous glands, which represent modified and very highly differentiated sweat-glands. They are branched, tubulo-alveolar glands (Huber). They empty either into the hair follicles near the surface of the skin or on to the surface of the skin in the neighborhood of the hair follicles.
The skin lining the osseous portion of the external auditory canal is supplied with neither hair nor glands, and possesses slender papillae, especially in the neighborhood of the tympanic membrane. The corium is closely attached to the periosteum.
The tympanic membrane consists of a tense and a flaccid portion. It forms a part of both the external and the middle ear. From without inward, the following layers may be differentiated : (i) the cutaneous layer ; (2) the lamina propria ; and (3) the mucous layer.
The epidermis of the cutaneous layer is identical in structure with that of the outer skin, except that the superficial layers of the stratum corneum contain nucleated cells. The corium is very thin, except along the course of the manubrium of the malleus, where it
THE EXTERNAL EAR.
477
is thickened, forming the so-called cuticular ridge, which possesses papillae and is supplied with vessels and nerves.
The lamina propria ends peripherally in a thickened ring of fibroelastic tissue, the annulus fibrosus, which unites at the sulcus tympanicus with the periosteum of the latter. The lamina propria is composed of connective-tissue fibers, in which two layers may be distinguished externally, the radiate fibers, the stratum radiatum, and internally, the circular fibers, the stratum circulars. The external radiate layer extends from the annulus to the umbo and manut>rium, and is interrupted in the flaccid portion of the tympanic
Pinna.
BH W W
Fig. 366. Schematic representation of the complete auditory apparatus (Schwalbe).
membrane by the upper fourth of the manubrium and the short process of the malleus ; it gradually thins out toward the center until it finally disappears in the vicinity of the umbo. The fibers of the inner (circular) layer are circularly disposed. This layer is thickest at the periphery of the tympanic membrane, becoming gradually thinner toward the lower end of the manubrium, where it disappears. Between the two layers of the lamina propria is a small quantity of loose connective tissue. The manubrium of the malleus is inclosed within the tympanic membrane. This is due to the union of the fibers of the radial layer with the outer strata of the manubrial perichondrium, the handle of the malleus being here covered by a thin layer of cartilage. In the posterior upper quadrant of the tympanic membrane the two layers of the lamina propria
THE ORGAN OF HEARING.
intermingle, forming irregularly disposed bundles and trabeculae, the dendritic fibrous structures of Gruber.
The mucous layer of the tympanic membrane consists of simple squamous epithelium separated from the lamina propria by a thin connective-tissue layer containing but few cells. It likewise extends over the handle of the malleus. In the flaccid portion of the tympanic membrane the lamina propria disappears, so that in this region the cutaneous layer and the mucous membrane are in direct contact.
B. THE MIDDLE EAR.
The middle ear, or tympanum, is a small irregular cavity, filled with air, situated in the petrous portion of the temporal bone between the bony wall of the inner ear and the tympanic membrane, and communicates with the pharynx through the Eustachian tube. It contains the small bones of the ear, their ligamentous attachments, and, in part, the muscular apparatus moving them.
The mucous membrane lining the tympanic cavity is folded over the ossicles and ligaments of the tympanum and is joined to that of the tympanic membrane and the Eustachian tube, the line of junction with the former being marked by the presence of papilla-like elevations.
The epithelium of this mucous membrane is a simple pseudostratified ciliated epithelium, having two strata of nuclei. Cilia are, however, lacking on the surface of the auditory ossicles, on their ligaments, and on the promontory of the inner wall, as well as on the tympanic membrane. The mucosa of the mucous membrane is intimately connected with the periosteum, and may now and then contain short isolated alveolar glands, especially in the neighborhood of the opening of the Eustachian tube.
The "auditory ossicles" are true bones with Haversian canals and lamellae ; with the exception of the stapes, they contain no marrow-cavity. Very distinct perivascular spaces are seen surrounding the vessels in the canals (Rauber). The malleus articulates with the incus, both articular surfaces being covered with hyaline cartilage. Within this articulation we find a fibrocartilaginous meniscus, and at the summit of the short limb of the incus another small cartilage plate. Between the lenticular process of the incus and the capitulum of the stapes is another articulation, also provided with cartilaginous articular surfaces. The basal plate of the stapes is covered both below and at its edges with cartilage, as are also the margins of the fenestra ovalis (fenestra vestibuli). The basal plate is held in place within the fenestra by an articulation, provided with tense ligamentous structures on the tympanic and vestibular sides. Between these the connective tissue is quite loose. All the cartilaginous portions of the auditory ossicles, with the ex
THE MIDDLE EAR.
479
ception of the articular cartilages, rest on the periosteum (Riidinger, 70).
Thcfenestra rotunda (fenestra cochleae) is closed by the secondary or inner tympanic membrane, a connective-tissue membrane containing vessels and nerves, the outer wall of which is covered by ciliated epithelium, the inner (the surface toward the scala tympani) by flattened endothelial cells.
In the antrum and mastoid cells, the mucosa of the mucous membrane is immovably fixed to the periosteum. The epithelium is of the simple squamous variety and is nonciliated.
Portion of Eustachian tube free from glands.
Cartilage. ^
Mucosa of the
pharynx.
Glands.
Glands. -. r^J
Fig. 367. Cross-section of the Eustachian tube with its surrounding parts ; X I2 (from a preparation by Professor Riidinger).
The mucous membrane of the osseous portion of the Eustachian tube is very thin, and its mucosa is intimately connected with the periosteum. Its epithelium is of the simple pseudostratified ciliated variety, having two strata of nuclei. There are rio glands. The mucous membrane of the cartilaginous portion of the Eustachian tube is thicker, and its epithelium, which is of the stratified ciliated variety, is higher, and often contains goblet-cells. Lymphoid tissue may be demonstrated in the mucosa of this portion, and occasionally structures resembling lymph-nodules are found, especially in the vicinity of the pharyngeal opening of the tube. In the cartilaginous portion of the. tube are mucous glands, which are particularly
THE ORGAN OF HEARING.
numerous in the vicinity of the pharyngeal opening (Riidinger, 72, 2). The cartilage of the Eustachian tube is in part yellow elastic^ in part hyaline, and in certain portions presents the appearance of white fibre-cartilage.
C THE INTERNAL EAR,
The internal ear consists of an osseous and a membranous portion, the osseous and the membranous labyrinths ; the latter is contained within the former, and, although smaller, presents the same
Superior semicircular canal.
Horizontal semicircular canal. Posterior semicircular canal.
Ampulla.
^^ ^^ ^~ " Bony cochlea.
Vestibule. Fenestra rotunda.
Fig. 368. Right bony labyrinth, viewed from outer side : The figure represents the appearance produced by removing the petrous portion of the temporal bone down to the denser layer immediately surrounding the labyrinth (from Quain, after Sommering).
general shape. The two structures are separated by a lymph-space containing the perilymph.
In the bony labyrinth we recognize a central portion of ovoid shape, known as the vestibule, the outer wall of which forms the inner wall of the tympanum and presents two openings, the fenestra ovalis and the fenestra rotunda, separated by a ridge known as the promontory. This ridge becomes continuous with the lower portion of the bony cochlea, anterior and mesial to the vestibule and having the shape of a blunt cone. From the posterior portion of the vestibule arise three semicircular canals, known respectively as the external or horizontal semicircular canal, the anterior superior vertical, and the posterior inferior vertical semicircular canals. The canals communicate with the vestibule by means of five openings, the superior contiguous portions of the anterior and posterior canals uniting to form the canalis communis before reaching the vestibule. The three canals present near their origin from the vestibule enlargements known as the osseous ampullae. The osseous labyrinth is lined throughout by a thin -layer of periosteum, covered by a layer of endothelial cells.
THE INTERNAL EAR.
48l
The membranous labyrinth differs in shape from the osseous labyrinth in that, in place of the single chamber (vestibule) of the latter, the membranous labyrinth presents two sacs, the utriculus and the sacculus, united by a narrow duct, the utriculosaccular duct. The utriculus is the larger, and from it arise the membranous semicircular canals. These present ampullae, situated within the osseous ampullae previously mentioned. The sacculus communicates with the cochlear duct by means of the canalis reuniens (Hensen). From the utriculosaccular duct arises the ductus endolymphaticus, which passes through the aqueductus vestibuli and ends in a subdural sacciis endolymphaticus on the posterior surface of the petrous portion of the temporal bone.
In the membranous labyrinth the nerves are distributed over certain areas known as the maculce, cristce, and papilla spiralis.
,' "i
Auditory nerve with its vestihular and cochlear branches.
Ant. semicircular canal. Ampulla.
Cochlear duct. Canalis reuniens. Ductus Ampulla. Horizontal semicir
endolymphaticus. cular canal.
Fig. 369. Membranous labyrinth of the right ear from five-month human embryo (from Schwalbe, after Retzius).
There is a macula within the recess of the utriculus, the macula acustica utriculi ; and another within the sacculus, the macula acustica sacculi ; cristae are present in the ampullae of the upper, posterior, and lateral semicircular canals, the cristce ampullares sup., post., et lat. Besides these, we have the terminal arborization of the acoustic nerve in the membranous cochlea, the papilla spiralis cochlece, or the organ of Corti.
3
482
THE ORGAN OF HEARING.
J. UTRICULUS AND SACCULUS.
Only the inner wall of the utriculus is connected with the periosteum of the vestibule. In this region lies the corresponding
Membranous semicircular canal.
Blood-vessel .
Wall of membranous
canal.
Epithelium of the
membranous canal.
Ligament of canal.
Bone.
Perilymphatic spaces.
I Blood-vessel.
Fig. 370. Transverse section through an osseous and membranous semicircular canal of an adult human being; y<^5 (after a preparation by Dr. Scheibe): a, Connectivetissue strand representing a remnant of the embryonic gelatinous connective tissue. Such strands serve to connect the membranous canal with the osseous wall.
macula cribrosa, through which the nerves penetrate to the macula of the utriculus. The utriculus and sacculus fill only a part of the inner cavity of the osseous vestibule. Between the osseous and membranous portions remains a space traversed by anastomosing connective -tissue trabeculae, and lined by endothelium, which also forms an investing membrane around the trabeculae. These trabeculae pass on the one side into the periosteum lining the vestibule, and on the other, into the wall of the utriculus and sacculus. The cavity which they thus traverse represents a perilymphatic space. (Compare Fig. 370, which shows analogous relations in the semicircular canals.)
The wall of the utriculus, especially its inner portion, consists of dense fibrous connective tissue, most highly developed in the region of the macula acustica. In the immediate vicinity of the
THE INTERNAL EAR. 483
macula utriculi the epithelium of the utriculus is high columnar in type ; in the remaining portion it consists of a single layer of low columnar cells, with a distinct basement membrane ; the epithelium of the macula itself is also high, and is composed of two kinds of elements of sustentacular elements and of the so-called auditory hair-cells. The sustentacular cells are tall epithelial cells resting on the basement membrane by means of their single or cleft basal plates. Each possesses an oval nucleus lying at or beneath the center of the cell. The hair-cells are peculiar cylindric elements with somewhat thickened and rounded bases. One end extends to the surface of the epithelium, while the other, which contains the nucleus, extends only to the center of the epithelial layer. The free end is provided with a cuticular zone supporting a number of long, stiff hairs, which often coalesce to form single threads. On the surface of the epithelium, which must be regarded as a neuro-epithelium, are crystals of calcium carbonate, known as oto-* lit/is, each of which incloses a minute central vacuole (Schwalbe). The otoliths are inclosed in a homogeneous substance, the otolithic membrane, which coagulates in a network of filaments when subjected to the action of fixing agents.
The nerve-fibers going to the macula penetrate the wall, and, under the epithelium, undergo dichotomous division, and, after further division, form, in the region of the basilar ends of the auditory cells, a plexus consisting of fine ramifications, and embracing the lower ends of the auditory cells. A few fibers extend still further upward, where their telodendria enter into intimate relations with the acoustic cells (v. Lenhossek, 94, i).
The structure of the sacculus is in every respect like that of the utriculus, and a further description of it is therefore unnecessary.
2. THE SEMICIRCULAR CANALS.
The membranous semicircular canals are attached at their convex surfaces to the periosteum of the bony canals, which they only partly fill, the remaining cavity being occupied by an eccentrically situated perilymphatic space traversed by connective-tissue trabeculae. The walls of the perilymphatic spaces of the semicircular canals, like those surrounding the utriculus and the sacculus, are lined by endothelium, which covers, on the one hand, the periosteal surface of the bony semicircular canals, and, on the other hand, the outer wall of the membranous canals, together with the connective-tissue trabeculae. The connective-tissue walls of the membranous canals are structurally similar to those of the utriculus and sacculus. Hensen compares their structure to that of the substantia propria of the cornea. In the adult, the inner layer of the wall of the canals supports here and there papillary elevations, which, however,
4 8 4
THE ORGAN OF HEARING.
disappear along its attachment to the bony semicircular canal (Riidinger, 72, 88).
The epithelium lining the membranous semicircular canals is simple squamous in character and very evenly distributed over the entire inner surface, including the papillae previously mentioned.
On the concave side of each semicircular canal the epithelial cells are somewhat narrower and higher. This inner and higher epithelium (raphe), extending along the concave side into the ampullae, marks the region at which the semicircular canals were constricted off from the pocket-like anlagen. The epithelium of the ampullae (Fig. 371), with the exception of that in the region of the raphe, is of the squamous type. At the cristae of the ampullae, however, there is found a neuro-epithelium similar to that of the maculae. The cells adjoining both ends of the cristae are high columnar, and to these the squamous epithelium is joined. The columnar cells just mentioned form the so-called scmilunar fold. Otoliths are also present upon the neuro-epithelium of the cristae. Here the structure corresponding to the otolithic membrane of the utriculus and sacculus is called the cupula. In preserved specimens it presents the appearance of a coagulum, showing a faint striation ; in
the fresh condition, it has never been recognized as a distinct structure, at least in the lower classes of vertebrates.
' d
Fig- 37L Part of a vertical section through the anterior ampulla, showing the membranous wall, a portion of the "crista acustica," and the "planum semilunatum" (after Retzius) : a, Semilunar fold ; 6, crista acustica ; t, nerve-fibers ; d, bloodvessels.
3. THE COCHLEA.
The cochlea consists of an osseous portion, the bony cochlea, a membranous portion, the cochlear duct, and two perilymphatic canals. The bony cochlea consists of a central bony axis of conical shape, the modiolus, around which is wound a spiral bony canal, having in man a little over two and one-half turns, the modiolus forming the inner wall of this canal. The summit of the cochlea, which has the shape of a blunt cone, is formed by the blind end of this bony canal, and is known as the cupola. The modiolus further gives support to a spiral plate of bone, the lamina spiralis ossea, which extends from the lower part of the modiolus, and, forming two and one-half spiral turns, reaches its top, where it ends in a hook-like process, the hamulus. This bony spiral lamina partly
THE INTERNAL EAR. 485
divides the bony cochlear canal into two parts, the division being completed by a fibrous tissue membrane, the lamina spiralis membranacca, which extends from the free edge of the osseous spiral lamina to a thickened periosteal ridge, the ligamentum spirale, lining the outer wall of the bony cochlear canal. The canal above the lamina spiralis (bony and membranous) is known as the scala vestibuli, that below as the scala tympani. Both are perilymphatic canals, and communicate in the region of the last half-turn of the cochlea, by means of a narrow canal, the helicotrema, partly surrounded by the termination of the bony spiral lamina, the hamulus. The scala vestibuli is in free communication with the perilymphatic space of the vestibule ; while the scala tympani communicates with perivascular spaces surrounding the veins of the cochlear aqueduct, which latter empty into the jugular veins. The scala tympani terminates at the secondary tympanic membrane, closing the fenestra rotunda.
The cochlear duct, which, as will be remembered, communicates with the sacculus by means of the canalis reuniens, is a long tube closed at both ends,' the one end representing the vestibular sac, or ccecum vestibulare, and the other the cupolar extremity, or cacum cupolare, also known as the lagena. The cochlear duct forms about two and three-fourths spiral turns, its length being about 3.5 mm. Its diameter gradually increases from its lower to its upper or distal extremity. The cochlear duct lies above the lamina spiralis, and, in a section of the cochlea parallel to the long axis of the modiolus, it is of nearly triangular shape, with the somewhat rounded apex of the triangle attached to the osseous lamina spiralis. In the cochlear duct we may distinguish the following parts : (i) the outer wall, which is intimately connected with the periosteum of the bony cochlear canal ; (2) the tympanal wall, resting on the membranous basilar membrane, with its highly differentiated neuro-epithelium, the spiral organ of Corti ; and (3) the vestibular wall, bordering on the scala vestibuli, the intervening structures forming a very delicate membrane the vestibular or Rcissnci- ' s membrane.
From the account given thus far, it may be seen that within the bony cochlear canal there are found three membranous canals, running parallel with one another and with the osseous lamina spiralis about which they are grouped. Two of these membranous canals, the scala vestibuli and the scala tympani, are perilymphatic spaces, and are consequently lined by endothelial cells ; between them is found the cochlear duct, from its position known also as the scala media, lined by epithelial cells. These three membranous canals retain their relative position in their spiral course about the modiolus, and, in a section through the cochlea parallel to the bony axis of the modiolus, would be met with at each turn, and at each turn present essentially the same relative position and structure. In figure 372, which is from a longitudinal section of the cochlea
486
THE ORGAN OF HEARING.
of a cat, the general relations of the parts are clearly shown. Figure 373 is sketched from a longitudinal section of the cochlea of a guineapig, and shows the appearance presented by a section through one of the turns of the bony cochlear canal and its contents as seen under higher magnification. We may now proceed with a fuller consideration of the structures mentioned.
msp
Kn
Fig. 372. Longitudinal section of the cochlea of a cat ; X 2 5- This figure giresa general view of the cochlea. The cochlear duct is met with six times in the section : dc t cochlear duct ; gsp, spiral ganglion ; Kn, osseous cochlear wall ; Isp, ligamentum spirale ; msp, membrana spiralis; mv, membrana vestibularis or Reissner's membrane ; , nervus cochlearis; set, scala tympani; scv, scala vestibuli (Sobotta, "Atlas and Epitome of Histology").
The lamina spiralis ossea consists of two bony plates which inclose between them the ramifications of the cochlear nerve. The vestibular surface of the osseous lamina spiralis is covered by periosteum, which is continuous with a peculiar tissue, known as limbus spiralis. The latter begins at the point of attachment of Reissner's
THE INTERNAL EAR.
487
membrane, extends peripherally (externally), and ends in two sharp ridges, of which the shorter, the labium vcstibulare, projects into the inner space of the cochlear duct and continues into the tectorial membrane ; while the other and longer, the labium tympanicum, becomes attached to the wall of the scala tympani and continues into the basilar membrane. Between the two ridges is a sulcus, the sulcus spiralis interims. (Fig- 373-) The limbus spiralis
Fig. 373. Section through one of the turns of the osseous and membranous cochlear ducts of the cochlea of a guinea-pig ; X 9 : ?> Scala vestibuli ; m, labium vestibulare of the limbus ; , sulcus spiralis internus ; o, nerve-fibers lying in the lamina spiralis ; /, ganglion cells ; q, blood-vessels ; a, bone ; b, Reissner's membrane ; DC, ductus,
cochlearis ; d, Corti's membrane;/", prominentia spiralis; g, organ of Cord; h, ligamentum spirale ; i, crista basilaris ; k, scala tympani.
is a connective-tissue formation in the region of the cochlear duct connected with the periosteum of the osseous spiral lamina and extending from the point of attachment of Reissner's membrane to the labium tympanicum. The tissue of the limbus spiralis is dense and richly cellular, and simulates in its structure the substantia propria of the cornea. A casual view would seem to disclose
488 THE ORGAN OF HEARING.
a high columnar epithelium, but upon closer observation, it is seen that the cellular elements are interspersed with fibers which extend to the surface. Some investigators regard this tissue as fibrocartilage ; others, again, as a tissue sui generis, consisting of epithelial cells mingled with connective-tissue fibers. If the labium vestibulare of the limbus spiralis be examined from the vestibular surface, a number of irregular tubercles are seen at its inner portion (near Reissner's membrane), while at its outer portion long, radially disposed ridges may be observed, the so-called auditory teeth of Huschke. The connective-tissue wall of the sulcus spiralis internus consists of a nonnucleated fibrillar tissue which is continued into the labium tympanicum. The latter is perforated by nerves, thus giving rise at this point to the foramina nervosa,
Between the point of attachment of Reissner's membrane and the labium vestibulare, the superficial epithelium of the limbus spiralis is flat, and lines the auditory teeth and the depressions between them in a continuous layer. The epithelium of the sulcus spiralis internus is somewhat higher.
The ligamentum spirale forms the thickened periosteum of the outer wall of the osseous cochlear canal. It presents two inwardly projecting ridges, the crista basilaris, to which the membranous lamina spiralis is attached, and the promincntia spiralis, which contains one or several blood-vessels ; between the two ridges lies the sulcus spiralis externus. The portion of the ligamentum spirale forming the periosteum of the bony cochlear canal consists of a fibrous tissue containing many nuclei, but changes internally into a looser connective tissue. The connective tissue lying external to the outer wall of the cochlear duct is veiy dense and rich in cellular elements and blood-vessels, but in the crista basilaris it changes to a hyaline, noncellular tissue, continuous with the lamina basilaris. That portion of the spiral ligament lying between the prominentia spiralis and the attachment of Reissner's membrane is known as the stria vascularis. The epithelium covering this area (a portion of the epithelium lining the cochlear duct) consists of columnar, darkly granulated cells, which now and then are arranged so as to present the appearance of a stratified epithelium, but which is more correctly interpreted as an epithelium of the pseudostratified variety. This epithelium shows no distinct demarcation from the underlying connective tissue. Beneath this epithelium there is found a rich capillary network, certain loops of which extend into the epithelium (Retzius). It is thought that the stria vascularis is concerned in the formation of the endolymph of the cochlear duct.
The membranous lamina spiralis, or the basilar membrane, extends from the tympanic lip of the osseous spiral lamina to the crista basilaris of the ligamentum spirale.
As already stated, the tissue composing the labium tympanicum of the limbus extends into the basilar membrane. In this
THE INTERNAL EAR. 489
membrane the surface toward the cochlear duct is known as the cochlear surface, that toward the scala tympani as the tympanic surface. Two layers are differentiated in the basilar membrane, the lamina basilaris propria and the tympanic investing layer. The lamina propria consists, in turn, of (i) radially arranged basilar fibers, or acoustic strings ; (2) two thin strata of a homogeneous substance, one above and the other below the layer of basilar fibers, the upper of which is the thicker and nucleated ; and (3) a fine cuticula, of epithelial origin, lying on the cochlear side. The tympanic investing layer is highly developed in youth, but later becomes thinner, and may then be differentiated into a connective-tissue layer, regarded as a periosteal continuation of the tympanic portion of the osseous lamina spiralis, and an endothelial cell layer belonging to the lining of the perilymphatic space or the scala tympani. In the vicinity of the labium tympanicum is a bloodvessel situated within the tympanic investing layer of the basilar membrane the vas spirale.
Reissner's membrane consists of an exceedingly thin connective- ' tissue lamella, lined on the side of the cochlear duct by a layer of flattened epithelial cells and on the vestibular side by a layer of endothelial cells. The epithelium lining the cochlear duct is occasionally raised into small villus-like projections.
The Organ of Corti. In the region of the labium tympanicum of the limbus spiralis and in the greater portion of the adjoining basilar membrane, the epithelium of the cochlear duct is peculiarly modified, forming here a neuro-epithelium, which receives the terminal ramifications of the cochlear nerve and is known as the spiral organ of Corti.
Passing from the labium tympanicum to the ligamentum spirale, the following three regions may be recognized in the organ of Corti : An inner region, composed of the inner sustentacular cells and the inner auditory cells ; a middle region, consisting of the arches of Corti ; and an outer region, in which are found the outer auditory cells and the outer sustentacular cells or Deiters's cells. Two cuticular membranes are in close relationship to the organ of Corti : namely, the lamina reticrdaris and the mcmbrana tcctoria, or membrane of Corti.
In figure 374, a sketch of the organ of Corti and adjacent structures, it may be observed that the epithelium lining the sulcus spiralis internus (at the right of the figure) is of the pavement variety, and that the epithelium becomes gradually thicker until the organ of Corti is reached, where it becomes suddenly elevated in the form of a wall. In this, two varieties of cells are distinguished sustentacular cells and inner auditory cells. The sustentacular cells, which follow the flattened cells, become gradually higher from within outward and occupy three or four rows. Next come the inner auditory cells, cylindric elements, somewhat rounded and
490
THE ORGAN OF HEARING.
thickened at their nucleated basilar ends. The latter do not extend to the basilar membrane but end at about the level of the center of the inner pillars. At the free end of each cell is an elliptic cuticular zone, somewhat broader than the end-surface of the corresponding cell. In man about twenty rigid filaments, known as auditory hairs, are found resting on each elliptic cuticular zone. These are either arranged in a straight row or they describe a slight curve.
The middle division of the organ of Corti, the arches of Corti, consists of long slender structures, known as pillar cells, or, briefly, pillars, resting firmly upon the basilar membrane and forming an arch at the vestibular side of the latter. They surround, by the
\:;;
Fig. 374- Organ of Corti : At x the tectorial membrane is raised ; c, outer sustentacular cells ; d, outer auditory cells ; f, outer pillar cells ; g, tectorial membrane ; //,
inner sustentacular cells; i,p, epithelium of the sulcus spiralis internus ; k, labium vestibulare ; e, tympanic investing layer ; m, outer auditory cells ; , , nerve-fibers which
extend through the tunnel of Corti ; o, inner pillar cell ; q, nerve-fibers ; /;, b, basilar membrane ; a, epithelium of the sulcus spiralis externus ; r, cells of Hensen ; s, inner auditory cell ; /, ligamentum spirale (after Retzius).
union of their free ends, a space which, as seen in figure 374> appears triangular in section. This is the tunnel of Corti.
According to their position, w 7 e distinguish inner and outer pillars, the inner being more numerous than the outer. Including the entire extent of the lamina spiralis membranacea, we find that there are about 6000 of the inner and 4500 of the outer pillar cells.
Each pillar cell originates from an epithelial cell, and is found to be composed of a protoplasmic portion containing the nucleus, which may be regarded as a remnant of the primitive cell, and of a cuticular formation derived from the primitive cell, forming the elongated body of the pillar cell the pillar. The free adjoining ends are called the heads of the pillars. The head of the inner pillar is provided with a flattened process, the head-plate, which extends outward and forms an obtuse angle with the axis of the pillar. Under this plate, and at the outer side of the head of the
THE INTERNAL EAR. 49!
inner pillar, is a depression into which fits the head of the outer pillar. The latter also extends outward in the shape of a phalangeal plate, with a thinner process, the phalangeal process, at its end. The phalangeal plate and process lie under the head-plate of the inner pillar, the process extending a little beyond this, forming an acute angle with the head of the outer pillar. At the inner side of the head of the outer pillar is a convex articular surface, with which, as a rule, two, and occasionally even three, articular surfaces of the inner pillars come in contact. The outer and inner pillars appear to possess an indistinct longitudinal striation, and their basilar plates are continuous with the extremely fine cuticula covering the basilar membrane. The inner margins of the basilar plates belonging to the inner pillars border on the foramina nervosa ; while the outer margins of the basilar plates belonging to the outer pillars come in contact with the basal end of the innermost row of the cells of Deiters in the outer region of Corti's organ. The protoplasmic portions of the pillar cells, constituting what are known as basal cells, lie against the basilar plates of the corresponding pillars, i. e., on the basilar membrane, and partly cover the bodies of the pillars, especially the surfaces toward the tunnel.
In order to comprehend the relative position of the inner auditory cells to the inner pillars, it may be stated that one auditory cell rests upon every two inner pillars.
The outer region of Corti's organ is joined directly to the outer pillar cells, and consists of four rows of auditory cells alternating with an equal number of sustentacular cells or Deiters's cells. Following these structures and in contact with them are the outermost sustentacular cells, known as Hensen's cells.
The outer auditory cells have a structure similar to that of the inner auditory cells, but possess a more slender body. They do not extend as far as the basilar membrane, but end at a distance from the latter equal to about double their own length. The cuticular zone of each outer auditory cell likewise assumes the form of an ellipse, with its long axis pointing radially. The surface of this zone also is provided with about twenty stiff auditory hairs, arranged in the form of a decidedly convex arch, the convexity of which points outward. At a short distance from the cuticular zone of each outer auditory cell is a peculiar round body, found only in these cells, the significance of which is unknown.
Deiters's cells rest on the basilar membrane, and in shape resemble a flask with a narrow neck, known as the phalangeal process, the latter lying between the auditory cells. The nuclei of Deiters's cells lie in the upper parts of the thickened basal portions of these cells.
With each Deiters's cell there is associated a cuticular structure, which extends along the surface of each cell in the form of a thin
492 THE ORGAN OF HEARING.
fiber, the sustentacular fiber, and which is found partly within and partly without the cell. The sustentacular fiber begins near the center of the thicker basal portion of the cell-body and extends first into the cell itself, then passes to the surface, and, entering the phalangeal process, passes to the top of the cell and expands as a plate, to which the name phalangeal plate has been given. The latter is broader than the phalangeal process, and since, as we shall see, the phalangeal plates are joined to one another, as well as to the elliptically shaped cuticular zones of the outer auditory cells, there remains a space between the cells of Deiters and the auditory cells, as also between the outer pillars and the innermost of the outer auditory cells, known as Nuel's space. To the basal regions of the inner row of the cells of Deiters is joined the basal plate of the outer pillars of the arches of Corti.
Next to the outer row of Deiters's cells are the cells of Hensen, arranged in about eight radially disposed rows. They form an eminence which is high internally, but gradually decreases in height externally. The somewhat narrowed bases of Hensen's cells probably extend, without exception, to the basilar membrane. The free surfaces of these cells are likewise covered by a thin cuticular membrane. In man the cells of Hensen usually contain yellow pigment ; in the guinea-pig, as a rule, fat ; and in the rabbit, generally rudiments of sustentacular fibers. Externally the cells of Hensen grad^ ally change into elements of a more cuboid type the cells of Claudius, of which there are about ten rows, radially disposed. The surfaces of the latter also possess a cuticular margin ; the nucleus is at the center of each cell and pigment is also present. Darker elements with more basally situated nuclei sometimes occur between these cells, giving rise to the appearance of a double-layered epithelium (Bottcher's cells).
Thus far we have considered in detail the cells comprising the organ of Corti, and described their relative positions and sequence from within outward. In order to give a clearer understanding of the mutual relations of these cells, from within outward and in the direction of the spiral turning of the cochlea, we shall now consider the appearance presented in a surface view of the organ of Corti.
From within outward a surface view of the organ of Corti presents the following characteristics : The somewhat broadened hexagonal outlines of the inner sustentacular cells adjoin the epithelial elements of the sulcus spiralis internus and terminate externally in a spiral undulating line (if seen for only a short distance, this line appears straight). On this line border the contours of the cuticular zones belonging to the inner auditory cells. The outer margins of the cuticular zones come in contact with the head-plates of the inner pillars, the cuticular zone of one inner auditory cell coming in contact with at least two head-plates. The externally directed processes of the head-plates belonging to the inner pillars come in contact with one another and end in a spiral line which for a short
THE INTERNAL EAR.
493
distance is apparently straight. The head-plates of the inner pillars cover the head-plates of the outer pillars (which also come in contact with each other), also their phalangeal plates, but not their phalangeal processes, which thus project beyond the line formed by the outer borders of the head-plates of the inner pillars. It should be mentioned that about three head-plates belonging to the inner pillar cells are in apposition to every two head-plates and their phalangeal processes of the outer pillar cells. The succeeding four rows, from within outward, are made up of alternately placed cuticular zones of the outer hair cells and the phalangeal plates of the Deiters's cells, alternating like the squares of a chess-board. This regular arrangement is lost in the outer row of Deiters's cells. The cells of Hensen adjoin this row, and when viewed from the surface, present the appearance of irregular polygons.
This arrangement is, however, seldom found to be as typical as that just described ; although the relations of the cells to one another always correspond in general to the foregoing scheme.
In the cupolar and vestibular sacs the neuro-epithelium changes into an epithelium of an indifferent type.
The lamina reticularis is formed by the cementing together of the phalangeal processes of the outer pillars and the phalangeal plates of Deiters's cells, and is continued externally by a cuticular membrane which covers the cells of Hensen and, as a much thinner cuticular membrane, extends over the cells of Claudius. In this membrane there are found three or four rows of small apertures, into which the outer hair cells project.
The membrana tectoria Cortii is attached to the limbus spiralis, but
becomes free at the margin of the labium vestibulare and thickens considerably, again becoming thinner toward its free end.
Fig. 375. Surface of the organ of Corti, with the surrounding structures, from the basal turn of the cochlea of a new-born child ; the original drawing reduced one-half (after Retzius, 84): a, Epithelium of the sulcus spiralis externus ; b, Hensen' s cells; c, terminal frame; d, phalanges ; /, outer auditory cells; g, flattened processes of the outer pillar cells ; h, flattened processes of the inner pillar cells ; i, inner auditory cells ; k, inner sustentacular cells ; /, epithelium of the sulcus spiralis interims ; in, margin of the labium vestibulare ; , epithelium of the limbus laminae spiralis ; o, line of attachment of the membrana Reissneri ; /, epithelium of the membrana Reissneri, the latter inverted.
494 THE ORGAN OF HEARING.
Hence an inner attached and an outer free zone may be differentiated. This membrane has no nuclei, and shows a fine radial striation. Its free portion bridges over the sulcus spiralis internus and rests upon the organ of Corti. Its outer margin extends as far as the cells of Hensen. The development of this membrane is not thoroughly understood, although it very probably represents a displaced cuticular formation belonging to the cells of the limbus spiralis. This acceptation has recently been confirmed (Exner).
The auditory nerve gives off, soon after entering the internal auditory meatus, vestibular branches to the maculae in the utriculus and sacculus and to the cristae in the semicircular canals, and a cochlear branch, which passes up through the modiolus in anastomosing bony canals. From this centrally placed column of nervefibers, a continuous sheet of nerve -fibers, arranged in the form of anastomosing bundles, passes radially into the osseous spiral lamina and thence to the organ of Corti. Near the base of the osseous spiral lamina, along the entire length of this sheet of nerve-fibers, there is situated in a special bony canal a ganglion, known as the spiral ganglion of the cochlea. The ganglion cells of this ganglion are bipolar, one of the processes of each cell, the dendrite, extending outward through the osseous spiral lamina to the organ of Corti, the other process, the neuraxis, passing through the bony canal in the modiolus, through the internal auditory meatus, and thence to the medulla. The dendritic processes of the nerve-cells of the spiral ganglion form bundles of medullated nerve-fibers, which pass outward within the osseous spiral lamina, forming, in the outer portion of the latter, a closely meshed plexus, from which small bundles of nerve-fibers proceed through the foramina nervosa of the labium tympanicum to the organ of Corti ; immediately before passing through these foramina, the medullated nerve-fibers lose their medullary sheaths and neurilemma.
These nonmedullated fibers, with or without further dividing, are then arranged in small bundles, which, for a certain distance, have a spiral course : that is to say, parallel to the tunnel of Corti. One such spiral bundle is situated on the inner side of the inner pillars, under the inner row of hair cells ; another, on the outer side of the inner pillars, in the tunnel of Corti. Other fibers pass through the tunnel of Corti, so-called tunnel-fibers, to reach the outer side of the arches of Corti, where they are arranged in three or four spiral bundles, at the outer side of the outer pillars and between the rows of the cells of Deiters. From the nerve -fibers of these spirally arranged bundles, terminal branches are given off, which terminate, after further division, on the inner and outer hair cells (Retzius, Geberg).
Regarding the blood-vessels of the membranous labyrinth, it should be mentioned that the internal auditory artery is a branch of the basilar artery, and divides into the rami vestibulares and rami cochleares. The branches of the former accompany those of the auditory nerve as far as the utriculus and sacculus. At the maculae
THE INTERNAL EAR.
495
and cristae the capillary networks are numerous and finely meshed, but in the remaining portions of the utriculus, sacculus, and semicircular canals, they form coarser networks. The cochlear branch accompanies the divisions of the auditory nerve as far as the first spiral turn of the cochlea ; the arteries supplying the remaining turns enter the axis of the modiolus, where they divide into numerous branches. The latter are coiled in a peculiar manner, forming the so-called glomeruli arteriosi cochlea. From these, branches are given off which penetrate the vestibular wall of the lamina spiralis ossea, where they supply the limbus spiralis and the small quantity of connective tissue in the membrana vestibularis. Other branches surround the scala vestibuli, supply the walls of the latter, and then continue to the ligamentum spirale, the stria vascularis, and the lamina basilaris.
Fig. 376. Scheme of distribution of blood-vessels in labyrinth (after Eichler) :
g, Artery ; h, spiral ganglion ; z, vein ; v, scala vestibuli ; DC, ductus cochlearis ; c, capillaries in the ligamentum spirale ; d, capillaries in the limbus spiralis ; f, scala tympani.
The venous trunks lie close to the arteries and receive their blood from the veins which lie at the tympanal surface of the lamina spiralis and from those which encircle the outer wall of the scala tympani. The former, in turn, receive their blood from the capillaries of the limbus spiralis ; the latter, principally from the region of the ligamentum spirale and the basilar membrane.
From this description it is seen that the arterial channels are connected with the scala vestibuli, the venous with the scala tympani, and that the inner blood stream circulating through the lamina spiralis and limbus spiralis is separated from the blood current of the two scalae, the ligamentum spirale, and the crista basilaris (Eichler).
The entire membranous labyrinth is filled with endolympJi. The ductus endolymphaticus is, as will be remembered, a canal ending
496 THE ORGAN OF HEARING.
under the dura in a saccus endolympJiaticus. In connection with the latter are epithelial tubules bordering upon lymph-channels, with which they probably communicate by means of interepithelial (intercellular) spaces (Riidinger, 88). The efferent channels for the perilymph of the vestibule extend along the nerve sheaths of those nerves supplying the maculae and cristae ; these passageways finally communicate with the subdural or subarachnoid spaces. The perilymph of the cochlea is carried off by the adventitious tissue of the vena aqueductus cochleae, the lymph-vessels of which empty into certain subperiosteal lymph-channels near the inner margin of the jugular fossa.
4. ON THE DEVELOPMENT OF THE LABYRINTH.
In man the epithelium lining the membranous labyrinth originates from the ectoderm as a single-layered epithelial vesicle, the auditory vesicle or the otocyst, during the fourth week of embryonic life. After being constricted off from the ectoderm, this vesicle lies in the vicinity of the epencephalon and is surrounded by mesenchyme. The auditory vesicle then develops a dorsomesial evagination, which gradually grows larger and finally becomes the ductus endolymphaticus. An evagination also occurs in the ventral wall of the vesicle, the recessus cochlea. At the same time the mesial wall is pushed inward, thus incompletely dividing the vesicle into two smaller sacs the dorsal utriculus and the ventral sacculus. From the utricular portion there arises a horizontal evagination, flat and quite broad the first trace of the lateral or horizontal semicircular canal ; soon after, another evagination, vertical and still broader than the first, is seen the anlage of the other two canals. The outer portion of these pouches gradually expands, while in the middle, the two layers of each evagination come in contact with each other and coalesce, finally becoming absorbed. In the vertical evagination two such areas of adherence are found, thus forming a superior and a posterior canal, both having a common crus at one end.
The recessus cochleae grows both in a longitudinal and in a spiral direction, forming the cochlear duct.
In the immediate vicinity of the membranous labyrinth, the mesenchyme is differentiated into a connective-tissue wall for the former. The successive layers of mesenchyme, except in those areas where the membranous labyrinth later becomes adherent to the osseous, are transformed into a mucous connective tissue. The latter is surrounded by a more compact tissue, from which are derived, first, cartilage ; then bone and periosteum, and thus, finally, the osseous labyrinth. By a peculiar process of regressive metamorphosis most of the mucous connective tissue later disappears. In the adult it is replaced by the perilymphatic spaces of the labyrinth.
TECHNIC. 497
TECHNIC.
In the treatment of the external and middle ear the usual methods are employed. For the study of the epithelium in conjunction with the adjacent bone the tissue is fixed and then decalcified, or subjected to those fixing methods which accomplish both processes at the same time. The latter method, however, can be applied only to very small objects.
The manipulation of the membranous labyrinth, especially that of the adult, is a very difficult technical problem. Its isolation from the petrous portion of the temporal bone without injury can be accomplished only in well-advanced fetuses and in children, and even here a thorough knowledge of the situation of the parts in the petrous portion of the temporal bone is essential. Smaller animals, especially rodents, afford better specimens. In the latter, the semicircular canals and cochlea give rise to more or less distinct projections into the tympanic cavity. If the latter be opened, the situation of the parts may be ascertained from without. In the rabbit and guinea-pig, the entire cochlea projects into the tympanic cavity, and may be easily removed in toto with a strong knife, and, as the bony cochlea in these animals has very thin walls, it offers very little resistance to the decalcifying fluid (use, for instance, 3% nitric acid).
According to Ranvier's method (89), the cochlea is opened with a scalpel in a 2 C / C solution of osmic acid in normal salt solution. After twelve hours the cochlea is placed for decalcification in 2 % chromic acid, which is frequently changed. In guinea-pigs, for instance, decalcification is accomplished in a week.
According to the method of Retzius (84), the opened cochlea is treated for half an hour with a 0.5% aqueous solution of osmic acid, and then for the same length of time with a 0.5% aqueous solution of gold chlorid. The organ of Corti is then dissected out and examined as a whole, or cut after carefully removing the bone.
The labyrinth of the human adult is usually prepared as follows : The apex of the petrous portion of the temporal bone is removed and the upper semicircular canal, together with the cochlea, opened in Miiller's fluid ; in this solution the pyramid is left for three weeks ; during the first week the fluid is changed daily, and every two days during the following weeks. The specimen is then washed for twenty-four hours in running water, placed in 80% alcohol for two weeks, and finally in 96% alcohol for two days. The preparation is now ready for decalcification. This is done with 5% nitric acid, which is to be changed daily (ten days to two weeks). Then follows washing for two days in running water, carrying over into 80 % alcohol for twenty-four hours, then into 96% alcohol for from six to eight days, and, finally, infiltration and imbedding in celloidin (A. Scheibe).
The following method may also be employed with good results : The isolated pyramid with opened semicircular canal and cochlea is treated with Miiller's fluid for two days at room-temperature, and then for three weeks in a thermostat at 23 C. During the latter period, the fluid should be changed. The specimen is then washed for forty -eight hours in running water, treated for fourteen days with 80% alcohol, then for eight days with 96% alcohol, decalcified, and further treated as in the preceding method.
32
THE ORGAN OF SMELL.
Up to the present time it has been customary to cut sections in celloidin ; but the combined celloidin-paraffin method may also be employed with good results, and even the paraffin method, if great care be exercised in imbedding the tissue.
The nerve-fibers and nerve-endings of the cochlea may be stained with the chrome-silver method. For this purpose it is recommended to employ embryos or young fetuses.
X. THE ORGAN OF SMELL.
THE nasal cavity consists of the vestibule, the respiratory region with the accessory cavities, and the olfactory region.
The vestibule is lined by stratified squamous epithelium. In the region of the anterior nares are hairs, the sebaceous glands of which are markedly developed, while at the level of the cartilage mucous glands are also present. The stratified squamous epithelium ceases at the anterior end of the inner turbinate bone and at the inferior nasal duct.
The respiratory region possesses a simple pseudostratified, ciliated epithelium having two strata of nuclei and provided with goblet cells ; the direction of the ciliate movement is toward the posterior nares. Numerous leucocytes are usually found in the epithelium and in the underlying mucosa. Branched alveolar glands, having mucous and serous alveoli, are here present. Within the mucosa are highly developed vascular plexuses, more especially of a venous character. The accessory cavities are likewise lined by ciliated epithelium, the ciliate movement being directed externally.
The olfactory region is principally confined to the superior turbinate bone and to the nasal septum lying opposite, although in the immediate vicinity of the olfactory region a few small islands of the same epithelial type are found, either entirely isolated or connected with the principal region by narrow bridges. In a fresh condition the olfactory region may be differentiated from the surrounding tissue by its color, which is distinctly yellow in man. Its pigment is contained within the sustentacular cells described on the next page.
The epithelium of the olfactory region is of the columnar pseudostratified type, with several strata of nuclei, and consequently closely simulates a stratified columnar epithelium. Here we distinguish olfactory cells and sustentacular cells.
The olfactory cells occupy a peculiar position among the cells of special sense in that they represent true ganglion cells (Schultze, Golgi, Ehrlich, Ramon y Cajal). Within the epithelial layer they appear as spindle-shaped cells, with a spheric nucleus provided with a large nucleolus lying in the thickest portion of each cell. The nuclei of the different cells lie at varying levels in the middle stratum
THE ORGAN OF SMELL.
499
of the epithelial layer. Toward the nasal cavity, the cells terminate in blunt cones, upon each of which are several stiff hairs, the olfactory hairs. The basilar ends form true centripetal nerve-processes, neuraxes, which end in the peculiar telodendria constituting the glomeruli of the olfactory bulb. (See p. 422.)
The nuclei of the sustentacular cells are more oval and are situated at nearly the same level. These cells present the appearances of long columnar cells, which toward the basement membrane terminate in one or several processes. Between the basilar ends of these cells we find a layer of elements the broad nucleated bodies of which rest on the basement membrane, while their upper extremities terminate in short superficial processes.
The mucosa contains a large number of leucocytes as well as
- " >-< - ~ > ^ _ '", K
_~ =>a V >> -.'.-'.-.'-', v s ? A ,>?. : * L'A"';7-^ -">;., - i
HI" *'" . f -' -" ./**. ' v , --.'"*' '^^^|
Fig. 377. Portion of transverse section of the olfactory region of man; X I 5 ' *>
zone of olfactory hairs ; ep, epithelium ; 2, zone of oval nuclei ; j, zone of round nuclei ;
gl, olfactory or Bowman's glands; n, branch of olfactory nerve; tp, mucosa or tunica
propria with blood-vessels (Sobotta, "Atlas and Epitome of Histology").
numerous branched tubular glands, the so-called olfactory glands or the glands of Bowman. In man these are albuminous (serous) glands, and their cells sometimes contain pigment.
Jacobson's organ consists of blindly ending tubes, situated at the lower portion and at the outer side of the nasal septum. It is lined by an olfactory mucous membrane and receives a branch of the nasal nerve. This organ is rudimentary in man.
The capillaries spread out immediately beneath the basement membrane of the epithelium. In the submucous connective tissue, we find a relatively well developed vascular plexus, rich in venous vessels ; this plexus is especially marked at the posterior portion of the inferior turbinate bone, forming here a tissue which resembles erectile tissue.
5OO THE ORGAN OF SMELL.
A dense network of lymphatics ramifies throughout the mucous membrane, carrying the lymph to the pharynx and palate. These lymph-vessels may be injected through the subarachnoid space (Key and Retzius).
The nerves (trigeminal) are widely distributed in the epithelium, ramifying through both the respiratory and olfactory regions. After repeated divisions these nerves lose their medullary sheaths, and end in telodendria which are usually provided with terminal nodules, although some are found which end in mere filaments.
TECHNIC.
The nasal mucous membrane is fixed in situ with osmic acid or one of its mixtures, after which small pieces are removed. It should be mentioned that the nonmedullated fibers of the olfactory nerve assume a brownish color under this treatment, while the fibers of Remak do not (Ranvier, 89).
In order to isolate the epithelial elements, pieces of the mucous membrane are treated with the y$ alcohol of Ranvier. But since the prolongations of the olfactory cells (neuraxes) shrivel and curl in this fluid, Ranvier recommends that, after the epithelial cells have been macerated in ^ alcohol for one or two hours, they be treated with i <f c osmic acid for a quarter of an hour. If shreds be now placed in water and teased, the cells, together with their prolongations, may be isolated without the curling of the latter.
The chrome-silver method applied to the nasal mucous membrane of young animals and fetuses has been the means of establishing the important fact that the olfactory cells of the olfactory region are in reality peripherally situated ganglion cells.
INDEX.
ABBE'S apparatus, 19
Absorption of fat by intestine, 288
method of studying, 306 Accessory disc of Engelman, 139
lacrimal glands, 470
thread of spermatosome, 361 Acervulus, 423 Acetic acid, effect on connective tissue,
128 on red blood-corpuscles, 188
sublimate solution as fixing fluid, 25 Achromatic portion of nucleus, 63
spindle, 68
Acidophile granules, technic for, 227 Adenoid connective tissue, 196 Adipose tissue, 107
stain for, 130
Agminated lymph-nodules, 197 Air-cells, 314 Air-spaces, ultimate, 313 Akrosome, 377 Alcohol as fixing solution, 23
as macerating solution, 22 Alcoholic borax-carmin solution as stain,
4i
in bulk, 46 Alkalies, effect on red blood-corpuscles,
189 Altmann's method of demonstrating
granules in cells, 77 of mounting, 78 process, 55 Alum-carmin as stain, 42
in bulk, 46
Alveolar ducts, 314, 315 glands, 91
compound branched, 91 simple, 91
branched, 91 periosteum, 242 Alveoli, 88 lung, 314
of mammary gland, epithelium of, 401 Amacrine cells, 464 Amitosis, 64, 70 Amitotic cell-division, 70 Amphiaster, 68 Amphipyrenin, 63
Amphophile granules, technic for, 228 Ampullae of Thoma, 204 Anaphases, 65, 69 Anastomoses, 222 Anilin stains, 44
Animals, injection of, 54 Anisotropic transverse disc, 138 Annulospiral nerve-ending, 178 Annulus fibrosus, 477
atrioventricularis, 214 Anterior epithelium of crystalline lens 468
ground bundle, 411
hyaloid artery, 468
lymph-channels of eye, 469
superior vertical canal, 480 Anterolateral columns, ascending, 411
descending, 411 Antrum of ovary, 347 Anus, 281 Apathy's method for demonstration of
fibrillar elements of nervous system,
442
Apochromatic lens, 19 Aponeuroses, 105 Aqueous borax carmin solutions as stain,
4i
humor, 446 Arachnoid, 437 Arches of Corti, 490 Arcuate fibers of cornea, 450 Area cribrosa, 332
vasculosa, 186 Areas of Langerhans, 301 Arrectores pilorum, 393 Arteriae arciformes, 332
capsulares glomeruliferas, 334 Arterial circle of Zinn, 465
retia mirabilia, 333 Arteries, 216
coronary, 214
hyaloid, anterior, 468 posterior, 468
interlobular, of kidney, 332
medium-sized, 218
of choroid, 455
of retina, 466
precapillary, 218 Arteriolse rectae spuriae, 333
verae, 334 Artery, auditory, internal, 494
central, of retina, 465
hepatic, 293
nasal, inferior, of retina, 466 superior, of retina, 466
papillary, inferior, of retina, 466 superior, of retina, 466
renal, 332
501
502
INDEX.
Artery, temporal, inferior, of retina, 466
superior, of retina, 466 Ascending anterolateral columns, 411 Association fibers of cerebral cortex, 420 Astrocytes, 435
Atresia of ovarian follicles, 353 Atria, 314
Attraction-sphere, 62 Auditory artery, internal, 494
cells, outer, 491
hairs, 490
nerve, 494
ossicles, 478
teeth, 488
Auerbach's plexus, 286 Auriculoventricular valves of heart, 213 Axial canals of small intestine, 285
cords, 157, 1 60
fibrils of, demonstration of, 181
sheath, 176
thread of spermatosome, 361
sheath of, 361 Axillary glands, 398 Axis-cylinder, 159
naked, 160 Axis-fibrils, 157 Axolemma, 157
BAILLARGER'S striation, 421
Balsam, Canada, as mounting medium,
52 Bardeen's table for drawing of portions
of sections to be reconstructed, 57 Bars of intercellular cement, 86 Bartholin's ducts, 253
glands, 360 Basement membrane, 8r, 88
of small intestine, 278 Basic stains, 41 Basichromatin granules, 62 Basilar membrane, 488 Basket cells, 254 Baskets, fiber, of retina, 462 Basophile granules, 193 cells with, 209 technic for, 228
Bechtereff and Kaes' striation, 421 Benda's chromatoid accessory nucleus,
377
method for demonstration of medullary sheath, 442
selective neuroglia staining method,
445 Berkley's method of demonstrating nerves
of liver, 308
Berlin blue as injection fluid, 55 Bertini, columns of, 324, 330 Bethe's method of fixing methylene-blue
for nerve-fibers, 184 of staining neurofibrils and Golgi nets, 443
Bile capillaries, 290, 291, 292 demonstration of, 306 impregnation of, 307 effect on red blood -corpuscles, 188
Bile-ducts, 296
Bioblasts, 60
Biondi-Heidenhain triple stain, 46
Bipolar cells of cone-visual cells, 463
of rod-visual cells, 463 Bismarck brown as stain, 44 Bladder, 336 nerves of, 339 technic of, 343 Blastema, 64
Blastodermic layers, primary, 79 Blastomeres, 70, 79 Blood, 186
coagulation of, 195 Blood, cover-glass preparations, 227 current, behavior of blood-cells in, 196 demonstration of, through vessels,
231
elements of, method of examining, 227 films, Wright's method of staining,
229
formation of, 186 islands, 186 plasma, 187 platelets, 194
fixation of, 227 shadows, 188 sinus, 222
supply of bronchi, 316 of Fallopian tubes, 355 of heart, 214 of intestine, 283 of lymph-glands, 200 of salivary glands, 259 of spleen, 203 of thymus gland, 212 of thyroid gland, 320 of uterus, 357 technic of, 226 Blood-cells, behavior of, in blood current,
196
counting, 232
red, nucleated, containing hemoglobin, 208 staining of, 227
Blood-corpuscles, cover-glass preparations, 226
red, 187. See also Erythrocytes. technic of, 226
white, 191. See also Leucocytes. Blood-counting apparatus, Thoma-Zeiss,
232 Blood-forming organs, 186
technic of, 226 Blood-placques, 194 Blood-vessels, 186, 216 fetal, of eye, 468 in striated muscular tissue, 143 ' nerve supply of, 223 of bone-marrow, 210 of central nervous system, 439 of eyelid, 473 of kidney, 332 of liver, distribution of, demonstration,
306 examination of, 343
INDEX.
503
Blood-vessels of lung, 316
of membranous labyrinth, 494 of mucosa of large intestine, 284
of pelvis of kidney, 338
of small intestine, 284 of nasal cavity, 499 of optic nerve, 465 of ovary, 354 of pancreas, 302 of prostate, 370 of retina, 465 of sclera, 449 of stomach, 284 of suprarenal glands, 341 of teeth, 242 of testis, 367 Blutlymphdriisen, 200 Body-cell, 71 Bohmer's hematoxylin as stain for bulk,
46
hematoxylon, 42 Bone, 112 breakers, 120 calcium carbonate in, alkaline purpurin
as stain for, 132 canaliculi, 113 compact, of shaft, development of,
124 corpuscles, 113
Schmorl's method of staining, 133
Virchow's method of isolating, 134 decalcification of, 132
fluids used for, 132
v. Ebner's method, 133 development of, 116
endochondral, 116
intramembranous, 122 endochondral, 116 intracartilaginous, 116 intramembranous, 116, 122 lacunae of, 112, 113 lamellae, 113
composition, 114
method of examining, 131 lime-salts in, hematoxylin as stain for, 132
isolation of, 132 soft and hard parts, relation of,
method of studying, 132 spaces in, Ranvier's method for demonstrating, 132 structure of, 112 undecalcified, microscopic preparation
of, 131
Bone-cells, 112, 115 Bone-marrow, 207 blood-vessels of, 210 gelatinous, 210 red, 207 technic of, 234 yellow, 207, 210 Bony cochlea, 484
labyrinth, 480 Borax-carmin, alcoholic, 41
in bulk, 46 aqueous, 41
Bern's method of construction by
plates, 56
Bottcher's cells, 491 Boundary zone, choroid, 453 Bowman's capsule, 323
glands, 499
membrane, 449 Box for imbedding tissues, 28 Bronchi, 311
blood supply of, 316
branches of, 311
nerves of, 317
terminal branches of, 313 Bronchioles, 311
respiratory, 313
terminal, 314, 315 Brownian movement of cells, 61 Brticker's lines, 137 Brunner's glands, 265, 277 Budding, 64 Bulb hairs, 393 Bulbus oculi, 446 Burdach's column, 411 Btitschli's foam-structure, staining for, 79
CUPOLARE, 485
vestibulare, 485
Calcification of cartilages, in Camera lucida, 20 Canada balsam as mounting medium,
5 2 Canalicular system in cartilage, method
of demonstrating, 131
lymph, 1 02
Canaliculi of bone, 113 Canalis communis, 480 Capillaries, 220
bile, 290, 291, 292 demonstration of, 306 impregnation of, 307
demonstrating distribution of, 235
lymph, 224
of cerebellar cortex, 440
of cerebral cortex, 440
of sweat-glands, 397 Capsule, Bowman's, 323
lens, 468
of cartilage, gold chlorid as stain for,
I3 1
of glands, 92
of Glisson, 289
of lymph-glands, 198
of Tenon, 448
suprarenal, demonstration of, 343 Carmin as stain, 41
mass, cold, as injection fluid, 54 Carmin-bleu de Lyon, 45 Carnoy's acetic acid-alcohol-chloroform mixture, 23
acetic-alcohol mixture, 23 Carotid gland, 225 Cartilage, 108
calcification of, in
canalicular system in, method of demonstrating, 131
504
INDEX.
Cartilage, capsules of, gold chlorid as
stain for, 131 connective tissue in, picrocarmin as
stain for, 131
corrosive sublimate as fixative for, 130 cuneiform, 310 elastic fibers in, picrocarmin as stain
for, 131
fibre-elastic, no glycogen in, iodo-iodid of potassium
stain to demonstrate, 131 ground-substance of, change in, in hyaline, 108 of larynx, 310 of Wrisberg, 310 osmic acid a fixative for, 130 ossification of, in
Caustic potash as macerating solution, 22 Cell, 58
absence of membrane, 62 air-, 314 amacrine, 464 auditory, outer, 491 basket, 254
blood, behavior of, in blood current, 196
counting of, 232
red, nucleated, containing hemoglobin, 208
staining of, 227 body-, 71 bone-, 112, 115 Brownian movement of, 61 centro-acinal, 300 chief, of acini of thyroid gland, 320
of hypophysis, 423 chromophilic, of hypophysis, 423 ciliated, 60
colloid, of acini of thyroid gland, 320 commissural, 408 cone-visual, 459
bipolar cell of, 463 connective-tissue, fat producing, 97
fixed, 103 cortical, small, of cerebellar cortex,
4iS
crystals of, 61 cuneate, 301 definition of, 58 Deiter's, 491 demilunar, 257 diagram of, 59 diffuse, of retina, 464 double staining of, 76 enamel, 243 endothelial, 80, 94
and mesothelial, method of studying relations, 95
demonstration of, 95
technic for, 233 epithelial, in small intestine, 275
isolated, examination of, 95 fat of, 61
fat-, scheme of, 107 fixing of chromic acid for, 75 corrosive sublimate for, 75
Cell, Flemming's solution for, 75
picric acid for, 75 flagellated, 60 follicular, 372 ganglion, 149
demonstration of, 182
of Dogiel, in spinal ganglia, 426 giant, 209 glandular, 61 glycogen of, 61 goblet, 87, 265
granular, of cerebellar cortex, 416 granules in, Altmann's method of
demonstrating, 77, 78 hair-, of utriculus, 483 hepatic, cords of, 290 horizontal, of retina, 464 liver-, examination of, 306 glycogen in, demonstration of, 306 lutein, 353 marrow-, 208 mast-, 104
granules of, technic for, 228 mesameboid, 80 mesothelial, 80
and endothelial, method of studying
relations, 95
migratory, 103, 104, 193 mitosis of, demonstration of, 75 mitral, 421
of olfactory bulb, 421 molecular movement of, 61 monostratified, of retina, 464 mother, 374 mucus-secreting, 87 muscle-, cardiac, demonstration of, 148
nonstriated, 134
of fibers of Purkinje, 147 nerve-, 149. See also Ganglion cell. neuro-epithelial, 92 neurogliar, 434 of Boucher, 492 of Claudius, 492 of column of Clark, 408 of Golgi, 408, 418, 419 of Hensen, 491, 492 of Langerhans, 300 of Leydig, 470 of Martinotti, 418, 419 of pancreas, inner and outer zones,
methods of differentiating, 308 of Purkinje, 153
of cerebellar cortex, 415 of reticular connective tissue, 100 of Sertoli, 364 olfactory, 498 parareticular, 464 pigment, 61, 77, 104 pillar, 490
heads of, 490
inner, 490
outer, 490 plasma, 104 plurifunicular, 408 polarity of, 81
INDEX.
505
Cell, polygonal, of cerebral cortex, 417 polymorphous, of cerebral cortex, 418 polynuclear, 70 polystratified, of retina, 464 pyramidal, large, of cerebral cortex,
417
of cerebral cortex, 153 small, of cerebral cortex, 417 rod-visual, 458
bipolar cell of, 463 seminal, primitive, 372 sense, 81
sexual, fertilization of, 71 male, development of, 72 matured, 7 1 somatic, 71 spider, 435
spindle-shaped, of cerebral cortex, 417 staining of, 76 stellate, large, of cerebellar cortex,
416
of cerebellar cortex, 415 of cerebral cortex, 417 of liver, 295
sustentacular, 92, 250, 372, 483 tendon, from tail of rat, 107 visual, 458
wandering, 60, 103, 104 with basophilic granules, 209 with eosinophile granules, 209 Cell-bodies of neurones, 149 Cell-body, 59 Cell-division, 64 amitotic, 70 direct, 64, 70 indirect, 64 karyokinetic, heterotypic, 374
homeotypic, 374 mitotic, of fertilized whitensh eggs,
66, 67
ten stages of, 65
Cell-masses, intertubular, of pancreas, 301 Cell-microsomes, 59 Celloidin imbedding, 30
diagram for, 32 infiltration, 30
diagram for, 32
sections, cutting of, with sliding microtome, 36
dextrin method of fixing, 40 Celloidin-parafnn imbedding, 32
infiltration, 32 Cell-plate, 70 Cell-spaces of areolar connective tissue,
102 Cellular elements of areolar connective
tissue, 103 Cement lines, 146 Cementum, 241, 246 Centers of ossification, 116 Central artery of retina, 465
gray nuclei of cerebellar cortex, 416 nervous system, 406 blood-vessels of, 439 fibrillar elements of, Apathy's method of demonstrating, 442
Central nervous system, lymph-vessels
of, 440
membranes of, 436 technic of, 440 spindle, 68 vein of retina, 465
Centripetal fibers of cerebral cortex, 420 Centro-acinal cells, 300 Centrosomes, 62, 427 Centrospheres, 62, 427 Cerebellar columns, direct, 411 cortex, 413
capillaries of, 440
central gray nuclei of, 416
granular layer of, 416
granular cells of, 416 large stellate cells of, 416 medullary substance of, 416 climbing fibers of, 416 mossy fibers of, 416 molecular layer of, 413
cells of Purkinje of, 415 small cortical cells of, 415 stellate cells of, 415 Cerebral cortex, 416 capillaries of, 440 medullary substance of, 419 association fibers of, 420 centripetal fibers of, 420 commissural fibers of, 420 projection fibers of, 419 stellate cells of, 417 molecular layer of, 417
polygonal cells of, 417 spindle-shaped cells of, 417 polymorphous cells of, 418 pyramidal cell of, 153 large, 417 small, 417
Ceruminous glands, 398, 476 Cervical canal, islands of ciliated epithelium in, 356 Chemotaxis, 61, 276 Chemotropism, 61 Chief cells of acini of thyroid gland, 320
of hypophysis, 423 Chlorate of potassium and nitric acid as
macerating solution, 23 Chondrin, method of obtaining, 112 Choroid, 446, 452 arteries of, 455 boundary zone of, 453 glassy layer of, 452, 453 lamina vasculosa Halleri of, 452 plexus, 439 Choroidal fissure, 447 Chromatin, 63
Chromatoid accessory nucleus of protoplasm of spermatid, 377 Chromatolysis, 74
technic, 74
Chromatophile granules, 149 Chromic acid as fixing solution, 26 as macerating solution, 22 for fixing cells, 75 Chromophilic cells of hypophysis, 423
506
INDEX.
Chromosomes, 67
daughter, 68
Chrzonszczewsky's physiologic auto-injection, 306 Chyle-vessels, 285 Cilia, 81, 470
movement of, method of observing, 95 Ciliary body, 446, 452, 453
nerve supply of, 456 glands, 398, 454
of Moll, 470 muscle, 454
meridional division, 454 middle division, 454 third or inner division, 454 processes, 453 Ciliated cells, 60
epithelium, islands of, in cervical
canal, 356
Circulation of hypophysis, 424 Circulatory system, 212
technic of, 235 Circulus arteriosus iridis major, 455
minor, 456 Circumanal glands, 398
of Gay, 282 Circumferential lamellae, inner, 113
outer, 113
Circumvallate papillae, 249 Clark's column, 408
cells of, 408 Claudius, cells of, 492 Clearing fluids, 52
Climbing fibers of cerebellar cortex, 416 Clitoris, 360 Cloquet's canal, 468 Club hairs, 393 Coagulation of blood, 195 Coal-tar stains, 44 Cochlea, 484 bony, 484 perilymph of, 496 spiral ganglion of, 494 technic for, 297 Cochlear duct, 484, 485 Cohnheim's fields, 140
method of impregnation, 48 Coil-glands, 396 Collective lens, 19
Colloid cells of acini of thyroid gland, 320 Colostrum, 402 '
corpuscles, 402 Columns, anterolateral, ascending, 411
descending, 411 cerebellar, direct, 411 lateral, 408
mixed, 411 of Bertini, 324, 330 of Burdach, 411 of Clark, 408 cells of, 408 of Goll, 411 of Gower, 411 of Sertoli, 364 pyramidal, crossed, 411 ventrolateral, 408
Columns, ventromesial, 408 Columnas rectales Morgagni, 282 Commissural cells, 408
fibers of cerebral cortex, 420 Commissures of spinal cord, 412 Compound microscope, 17 Concentric lamellae, 1 13 Concretions of prostate, 370 Condensers, 19 Cone-fibers of retina, 459 Cone-visual cells, 459
bipolar cells of, 463 Coni vasculosi Halleri, 364 Conjunctiva, 469
scleral, 448
Conjunctival portion of eyelids, 470 Connective tissue, 96
action of acetic acid on, 128 of hydrochloric acid on, 128 of potassium hydrate on, 128 adenoid, 196 areolar, 101
cell-spaces of, 102 cellular elements of, 103 ground-substance of, 102 matrix of, 102 development of, schematic diagram
of, 98 effect of pepsin on, 128
of trypsin digestion on, 127 fibrous, 101 white, 99 in cartilage, picrocarmin as stain for,
J3 1
magenta red as stain for, 128 mucous, 100 of liver, 294 orcein as stain for, 128 Ranvier's method for examination
of, 126 reticular, 100
cells of, 100 slide digestion of, 129 technic of, 126 Connective-tissue cells, fat producing, 97
fixed, 103 corpuscles, 103 fibrillae and reticulum, differential stain
for, 128
framework of organs and tissues, digestion method for demonstrating, 129
Contraction-ring, 158 Conus medullaris, 406 Convoluted tubules of testes, 363 Cord, spinal, 406 See also Spinal cord. Cords, axial, 157, 160
fibrils of, demonstration of, 181 hepatic, 290 medullary, 199 of hepatic cells, 290 pulp, 204 Corium, 379, 382 Cornea, 446, 449
anterior elastic membrane of, 449 arcuate fibers of, 450
INDEX.
507
Cornea, epithelium of, 449 ground plexus of, 45 1 nerves of, 451 technic, 474
perforating fibers of, 450 posterior elastic membrane of, 450 subepithelial plexus of, 45 1 substantia propria of, 449
technic, 474
superficial plexus of, 451 Corneal corpuscles, 450 epithelium, technic of, 474 spaces, 450
technic of, 474 Corona radiata, 347 Coronary arteries, 214 Corpora amylacea of prostate, 370
lutea spuria, 353 Corpus albicans, 353 Highmori, 363 luteum, 353
verum, 353 Corpuscles, blood-, red, 187. See also
Erythrocytes . blood-, white, 191. See also Leu~
cocytes. bone, 113
Schmorl's method of staining, 133 Virchow's method of isolating, 134 colostrum, 402 connective-tissue, 103 corneal, 450 genital, 171 Golgi-Mazzoni, 388 Grandry's technic of, 405 Hassal's, 212 Herbst's, 174, 389
technic of, 405
Malpighian, 202, 203, 323, 324 Meissner's, 170
technic of, 405 Pacinian, 388
technic of, 405 tactile, 387 Vater-Pacinian, 173
distribution of, 174
Corrosive sublimate as fixative for cartilage, 130
as fixing solution, 24 for fixing cells, 75 Cortex, cerebellar, 413. See also Cere bellar cortex.
cerebral, 416. See also Cerebral cortex. of ovary, 344 Cortical cells, small, of cerebellar cortex,
4i5
layer of hair, 389 nodules, 198
substance of kidney, 323, 324 Corti's arches, 490 membrane, 489, 493 organ, 481, 489 spiral organ, 489 Cover-slips, 20 fixing of large number of paraffin
sections to, 39
Cowper's glands, 370
Cox's method of impregnation, 51
Crescents of Gianuzzi, 256
Crista basilaris, 488
Crista?, 481
Crossed pyramidal columns, 411
Crosses, Ranvier's, demonstration of, 180
Crypts, Lieberkiihn's, 276
of stomach, 266 Crystalline lens, 467
anterior epithelium of, 468 Crystals, hematoidin, 231
hemin, method of obtaining, 230
hemoglobin, method of obtaining, 230
of cell, 6 1
Teichmann's, 188
method of obtaining, 230 Cuneate cells, 301 Cuneiform cartilages, 310 Cup, optic, 447 Cupola, 484 Cupula, 484 Currents of diffusion, 29 Cutaneous layer of tympanic membrane, 476
epidermis of, 476 Cuticle, 379
of hair, 389 inner, 389 Cuticula, 62, 81, 274
dentis, 238 Cuticular portion of eyelids, 470
ridge, 477
structures, 81
Cutis, 379. See also Skin. Cylindric end-bulb of Krause, 172 Czermak's interglobular spaces, 241 Czocor's cochineal solution, 42
DAMAR as mounting medium, 52 Daughter chromosomes, 68
nuclei, 64
stars, 374 Decalcification, 132
v. Ebner's method, 133 Decalcifying fluids, 132
aqueous solution of nitric acid, 133 hydrochloric acid, 132 Deiter's cells, 491 Delafield's hematoxylin, 43 Demilunar cells, 257 Demilunes of Heidenhain, 256 Dendrites, 149, 150
function of, 154 Dendritic fibrous structures of Gruber,
478
Dental sac, 244 Dentin, 239
development of, 244
fibrils of, demonstration of, 303 Dentinal fibers, 240
papillae, 243
tubules, 240 Dermis, 379, 382
508
INDEX.
Descemet's membrane, 450 endothelium of, 451 technic of, 474 Descending anterolateral columns, 411
limb of Henle's loop, 327 Deutoplastic granules, 349 Dextrin method of fixing celloidin sections, 40
paraffin sections, 40 Diapedesis, 193 Diaphragm, 17
iris, 1 8
Diaster, 69, 374 Diffuse cells of retina, 464
spongiblasts, 464 Diffusion, currents of, 29 Digestion method for demonstrating connective-tissue framework of organs and tissues, 129
slide, for connective tissue, 129 Digestive organs, 235 technic of, 303
tract, glands of, technic for, 304 Dilator muscle of pupil, 455 Direct cerebellar columns, 411
pyramidal tract, 411 Discus proligerus, 347 Dispirem, 69 Distilled water for fixing paraffin sections
to slide, 39 Dorsal utriculus, 496 Double knife, 21
staining, 44
of cells, 76 ' Doyere's elevation, 162 Duct, alveolar, 314, 315
Bartholin's, 253
bile-, 296
cochlear, 484, 485
ejaculatory, 368
excretory, 367
Gartner's, 360
intralobular, of pancreas, 300
nasal, 474
pancreatic, 298
Steno's, 253
utriculosaccular, 481
Wharton's, 253
Wirsungian, 298
Wolffian, 360
Ductus endolymphaticus, 476 Dura mater, nerves of, 437 spinal, 436
EAR, 476
external, 476 technic for, 497
internal, 480
middle, 478
technic for, 497
technic for, 497
vestibule of, 480 Ectoderm, 79
tissues derived from, 79 Egg tubes, primary, of Pniiger, 345
Ehrlich-Biondi-Heidenhain three-color
mixture, 229
Ehrlich's granulations, 227 hematoxylin, 43
for nuclei and granules, 228 leucocytic granules, 192 methylene-blue stain for nervous tissues,
182
neutrophile mixture, 229 Ejaculatory ducts, 368 Elastic elements, technic for, 235 fibers, 100
in cartilage, picrocarmin as stain
for, 131
respiratory, demonstration of, 322 membrane, anterior, of cornea, 449
posterior, of cornea, 450 tissue, effect of trypsin digestion on, 127
method of obtaining, 127 Enamel, 238 cells, 243 germs, 243 prisms, 238 technic of, 303 Encoche d' ossification, 121 End-brush, 162, 167, 237 End-bulbs of Krause, 170, 388
cylindric, 172 Endocardium, 213
lymphatic networks in, 215 Endochondral bone, 116 bone-development, 116 Endolymph, 495 Endomysium, 143 Endoneurium, 160 Endoplasm, 62, 98, 210 End-organ of Ruffini, 388 Endosteum, 207 Endothelial cells, 80, 94
and mesothelial cells, method of
studying relations, 95 demonstration of, 95 technic for, 233 Endothelium, 92
anterior, of iris, 455 of Descemet's membrane, 451 of intima, technic for, 235 End-piece of Retzius, 361 End-plate, motor, 163 Engelman, accessory disc of, 139 Entoderm, 58, 79
tissues derived from, 80 Eosin as stain for blood-cells, 227 Eosinophile granules, 193 cells with, 209 technic for, 227 Epicardium, 214 Epidermis, 379
nerves of, technic of, 405 of cutaneous layer of tympanic membrane, 476 technic of, 403 Epidural space, 437 Epilamellar plexus, 261, 397 Epimysium, 143 Epiphyses, development of, 121
INDEX.
509
Epiphysis, 422
Epithelial cells in small intestine, 275
isolated, examination of, 95 processes, interpapillary, 85 Epithelium, anterior, of crystalline lens,
468
ciliated, islands of, in cervical canal, 356 classification, 81, 82 columnar, pseudostratified, 83 simple, 83 stratified, 85 corneal technic of, 474 germinal, examination of, 378
of ovary, 345 glandular, 87 neuro-, 92
of alveoli of mammary gland, 401 of cornea, 449
of kidney, demonstration of, 343 of mucous membrane of intestine, 274
leucocytes in, 275 of vagina, 358 of olfactory region, 498 of urethra, 371 of vestibule of vagina, 360 posterior, of iris, 455 respiratory, 315
examination, of, 322 simple, 82 columnar, 83 cubic, 82 squamous, 82 stratified, 83 columnar, 85 squamous, 84 technic of, 94 transitional, 85 Eponychium, 395 Epoophoron, 344, 360 Erlicki's fluid, 26 Erythroblasts, 208 Erythrocytes, 187 diameter of, 190 effect of acetic acid on, 188 of alkalies on, 189 of bile on, 188 of fluids on, 188 of tannic acid on, 189 of water on, 188 examination of, 226 fresh, fixation of, 226 method of counting, 232, 233 size of, 190 stroma of, 187 technic for, 226 Esophagus, 262
method of examining, 305 Eustachian tube, 479
mucous membrane of, 479 Excavation, physiologic, of retina, 460 Excretory ducts, 367 Exoplasm, 62, 98, 210 External ear, 476
technic for, 497
External limiting membrane of retina, 459. 462
External semicircular canal, 480 Extra-epithelial glands, 88 Eye, 446
anterior lymph-channels of, 469
development of, 446
fetal blood-vessels of, 468
general structure of, 446
pigment membrane of, 446, 447, 457
protective organs of, 469
technic for, 474
tunica externa of, 446 fibrosa of, 446, 448 interna of, 446, 457 vasculosa of, 446, 452
tunics of, 446 Eyeball, 446
interchange of fluids in, 469 Eyelids, 469
blood-supply of, 473
conjunctiva! portion of, 470
cuticular portion of, 470
middle layer of, 471
third, 473'
FALLOPIAN tubes, 354 blood-supply of, 355 mucous membrane of, 354 muscular coat of, 355 treatment of, 378 Farrant's gum glycerin, 53 Fasciculus gracilis, 411 Fat, absorption of, by intestine, 288
method of studying, 306 lobules, 107 of cells, 6 1
Sudan III as stain for, 130 Fat-cell, scheme of, 107 Fat-marrow, 207 Female genital organs, 344
pronucleus, 74 Fenestra cochleae, 479 rotunda, 479 vestibuli, 478
Fenestrated membranes, 107 Ferrein, pyramids of, 324 Fertilization, process of, 71
diagrams of, 72, 73 Fetal blood-vessels of eye, 468 Fiber-baskets of retina, 462 Fiber-layer, Henle's, 461 outer of, retina, 461 Fibers, arcuate, of cornea, 450
association, of cerebral cortex, 420 centripetal, of cerebral cortex, 420 climbing, of cercbellar cortex, 416 commissural, of cerebral cortex, 420 cone-, of retina, 459 dentinal, 240 elastic, 100
in cartilage, picrocarmin as stain for,
I3 1
respiratory, demonstration of, 322 heart-muscle, MacCallum's nitric acid mixture for isolating, 23
5io
INDEX.
Fibers, lens, 468 mantle, 69
mossy, of cerebellar cortex, 416 motor, 162 Mtiller's, 454, 462 muscle-, intrafusal, 175
nonstriated, demonstration of, 148
striated, tcchnic of, 147
striped, 136
voluntary, development of, 144 nerve-, 157
ending in muscular tissue, 162
medullated, demonstration of, 180 of teeth, 242
methylene-blue stain for, 184
nonmedullated, 160 demonstration of, 182
of hair follicles, 393
of utriculus, 483 neuroglia, Benda's method of staining,
445
Mallory's methods of staining, 445 of olfactory nerve, staining of, 182 perforating, of cornea, 450 peripheral, of olfactory bulb, 421 projection, of cerebral cortex, 419 Purkinje's 213
isolated demonstration of, 148 muscle-cells of, 147 Remak's, 160
demonstration of, 182 reticular, of liver, demonstration of,
308
rod-, of retina, 458 Sharpey's, 115
method of isolating, 134 sustentacular, 492 terminal, of cerebral cortex, 420 tunnel-, 494 white, 99
rami, 429, 456 Fibrae circulares, 454 Fibril bundles, 140
Fibrillar elements of nervous system, Apathy's method for demonstration of, 442 Fibrils, axis-, 157
of axial cord, demonstration of, 181 of dentin, demonstration of, 303 Fibrin, demonstration of, 231 Fibrocartilage, white, no Fibro-elastic cartilage, no Fibrous connective tissue, 101
tissue elastic, 106 Filiform papillae, 248 Films, blood, Wright's method of staining, 229
Filum terminale, 406 Fimbriae linguae, 249 Fissure, choroidal, 447 Fixing methods, 23 solutions, 23
acetic sublimate, 25 alcohol, 23
Biitschli's foam-structure, for cells, 79
Fixing solutions, Carney's acetic-alcohol,
23
Carney's acetic acid-alcohol-chloroform, 23
chromic acid, 26 for cells, 75
corrosive sublimate, 24 for cartilage, 130 for cells, 75
Erlicki's, 26
Flemming's 24 for cells, 75
Fol's, 24
formalin, 27
formol, 27
Hayem's, 226
Hermann's, 24
Miiller's, 26
nitric acid, 26
osmic acid, 24 for cartilage, 130
picric acid, 25 for cells, 75
picric-nitric acid, 25
picric-osmic-acetic acid, 25
picric-sublimatc-osmic acid, 25
picrosulphuric acid, 25
potassium bichromate and formalin
27
Rabl's, 25 Tellyesnicky's, 26 vom Rath's, 25 Zenker's, 26 Flagellate cells, 60 Flagellum of spermatosome, 361 Flemming's germ centers, 194 solution, 24
for fixing cells, 75 Flower-like nerve-ending, 178 Fold, semilunar, 484 Foliate papillae, 249 Follicles, Graafian, 347
bursting of, 352 hair, 389
nerve-fibers of, 393 lymph-, germ centers of, technic for,
234 of mucosa of vermiform appendix,
281
of tongue, 251 of tonsils, 251 solitary, 197
technic for, 306 ovarian, atresia of, 353 simple, 197 Follicular cells, 372
glands, 91
Folliculi linguales, 251 Fol's solution, 24 Fontana's spaces, 455 Foramen apicis dentis, 238 Foramina nervosa, 488
papillaria, 330
Formalin as fixing solution, 27 Formol as fixing solution, 27 Fovea centralis, 460
INDEX.
Foveolae of stomach, 266 Fragmentation, direct, of nucleus, 71 Freezing apparatus for sliding microtome,
36
Friedlander's glycerin-hematoxylin, 43 Front lens, 19
Fuchsin-resorcin elastic fibers stain, 128 Fundamental lamellae, 113 Fundus glands of stomach, 268
of fovea centralis, 460 Fungiform papillae, 248 Funiculi, of nerve-trunk, 160
compound, 162 Funnels, pial, 439 Future periosteum, 116
GANGLIA, 424 spinal, 424 sympathetic, 427 Ganglion cell, 149
demonstration of, 182 layer of retina, 459, 464 of Dogiel, in spinal ganglia, 426 spiral, of cochlea, 494 Gartner's duct, 360 Gastric mucous membrane, 266 Gastrulation, 79
Gay's circumanal glands, 282, 398 Gelatin-Berlin blue as injection fluid, 54 Gelatin-carmin as injection fluid, 54 Gelatinous bone-marrow, 210 substance of Rolando, 408 Genital corpuscles, 171 organs, female, 344
male, 361 Genito-urinary organs, 323
technic of, 342
Gerlach's method of impregnation, 48 Germ center, 197
of Flemming, 194 of lymph-follicles, technic for, 234 enamel, 243 hair, 389 layers, 58
primary, 79 Germinal epithelium, examination of, 378
of ovary, 345 vesicle, 71 Giant cells, 209 Gianuzzi, crescents of, 256 Giraldes, organ of, 367 Gitterfasern, 301 Glands, alveolar, 91. See also Alveolar
glands. axillary, 398 capsule of, 92 carotid, 225 ceruminous, 389, 476 ciliary, 398, 454
Moll's, 470 circumanal, 282, 398 coil-, 396
extra-epithelial, 88 follicular, 91 hemal, 200
Glands, hemolymph, 200
structure of, 201 injection of, 55 intra-epithelial, 88 lacrimal, 473
accessory, 470
nerve supply of, 473 lenticular, 271 lymph-, 196, 197 . blood supply of, 200
capsule of, 198
hilum of, 197
lymph-sinuses of, 199
marrow, 201, 202
technic for, 233
trabeculae of, 198
with blood-sinuses, 200 mammary, 400. See also Mammary
gland. '
Meibomian, 472 mixed, 258 mucous, 255 multicellular, 88
classification, 91 of Bartholin, 360 of Bowman, 499 of Brunner, 265, 277 of Cowper, 370
of digestive tract, technic for, 304 of Gay, 282, 398 of Lieberkuhn's, 88, 276 of Moll, 398, 470 of Montgomery, 402 of mouth, small, 259 of oral cavity, 253 of skin, 396 of stomach, 267
cardiac, 267
fundus, 268 of Tyson, 372 parathyroid, 321 parotid, 255 peptic, 268 pineal, 422
prostate, 368. See also Prostate. pyloric, 269 salivary, 253, 255
blood supply of, 259
nerve supply of, 260 sebaceous, 398 serous, 255 splenolymph, 201 structure and classification, 88 sublingual, 255 submaxillary, 258
sudoriparous, 396. See also Sweatglands. suprarenal, 339. See also Suprarenal
glands.
sweat-, 396. See also Sweat-glands. tarsal, 472 thymus, 210
blood supply of, 212 thyroid, 319. See also Thyroid gland. tubular, 89. See also Tubular glands. tubulo-alveolar, 90
5 I2
INDEX.
Glands, unicellular, 87 Glandula carotica, 225 Glandulae buccales, 236
duodenales, 265
labiales, 236 Glandular cells, 61
epithelium, 87 Glassy layer of choroid, 452, 453
membrane of hair, 391 Glisson's capsule, 289 Glomerular layer of olfactory bulb, 421 Glomeruli arteriosi cochleae, 495 Glomerulus, 323 Glomus caroticum, 225 Glycerin, Farrant's gum, mounting in, 53
mounting in, 53
Glycerin-albumen for fixing paraffin sections to slide, 38
Glycogen in cartilage, iodo-iodid of potassium stain to demonstrate, 131
in liver-cells, demonstration of, 306
of cells, 6 1 Goblet cells, 87, 265 Gold chlorid as stain for capsules of cartilage, 131
method of impregnation, 48 Golgi-Mazzoni corpuscle, 388 Golgi-nets, Bethe's method of staining,
443 Golgi's cells, 408, 418, 419
chromsilver or chromsublimate method
of impregnation, 49
gold chlorid method of impregnation, 48 methods of impregnation, 49, 50 mixed method of impregnation, 50 potassium bichromate and bichlorid of mercury method of impregnation, 50
method of impregnation, 49 preparations, Huber's method of permanently mounting under coverglass, 51
rapid method of impregnation, 50 slow method of impregnation, 50 GolFs column, 411 Gower's column, 411 Graafian follicle, 347 bursting of, 352
Grandry's corpuscles, technic of, 405 Granular cells of cerebellar cortex, 416 layer of cerebellar cortex, 416 of olfactory bulb, 421 Tomes', 246 sole plate, 163
Granulations of leukocytes, 227 Granules, acidophile, technic for, 227 amphophile, technic for, 228 basichromatin, 63 basophile, 193 cells with, 209 technic of, 228 chromatophile, 149 deutoplastic, 349 eosinophile, 193 cells with, 209 technic for, 227
Granules, in cells, Altmann's method of demonstrating, 77, 78
indulinophile, technic for, 228
interstitial, Kolliker's, 141
leukocytic, Ehrlich's, 192
neutrophile, 193 technic of, 228
oxychromatin, 63
Schron's, 344
tigroid, 149
zymogen, in pancreas, demonstration
of, 308
Gray nuclei, central, of cerebellar cortex, 416
substance of spinal cord, 406, 409 Grenadier's alum-carmin, 42
as stain for bulk, 46 Ground bundle, anterior, 411
plexus of cornea, 451 Ground-substance interfascicular, 105
of areolar connective tissue, 102
of cartilage, changes, in, in Gruber's dendritic fibrous structure, 478 Gscheidtlen's method of obtaining hemoglobin crystals, 230 Gum glycerin, Farrant's mounting in, 53
HAIR, 389
auditory, 490
bulb, 389, 393
club, 393
cortical layer of, 389
cuticle of, 389 inner, 390
follicle, 389
nerve-fibers of, 393
germ, 389
glassy membrane of, 391
growth of, 392
medullary substance of, 390
olfactory, 499
papilla, 389
root, 389
root-sheaths of, 389 inner, 390 outer, 390
shaft, 389
shedding of, 393
technic for, 404 Hair-cells of utriculus, 483 Hamulus, 484 Hassal's corpuscles, 212 Haversian canals, 112
spaces, 1 20 Hayem's solution, 226
for diluting blood, 232 Hearing, organ of, 476. See also Ear. Heart, 186, 213
auriculoventricular valves of, 213
blood supply of, 214
elastic tissue of, 214
muscle, 145
motor nerve-supply of, 166
muscle-cells, demonstration of, 148
muscle-tissue, development of, 146
INDEX.
513
Heart, nerve supply of, 215 Heart-muscle fibers, MacCallum's nitric
acid mixture for isolating, 23 Heidenhain's demilunes, 256
iron hematoxylin, 43
as stain for bulk, 46
median membrane, 137 Helicotrema, 485 Heliotropism, 61 Heller's plexus, 283 Hemal glands, 200 Hemalum, acid, as stain, 43
as stain, 43
in bulk, 46 Hematin, 187 Hematoblasts, 194 Hematoidin crystals, 231 Hematoxylin as stain, 42. See also
Stains.
Hematoxylin-eosin as stain, 45 Hematoxylin-safranin as stain, 46 Hemin, 188
crystals, method of obtaining, 230 Hemocytometer, Thoma-Zeiss, 232 Hemoglobin, 187
crystals, method of obtaining, 230
demonstration of, 230
nucleated red blood -cells containing,
208
Hemokonia, 195 Hemolymph glands, 200
structure of, 201 Henle's fiber layer, 461
layer, 390
loop, 323
descending limb of, 327
sheath, 162 Hensen's cells, 491, 492
median disc, 137 Hepatic artery, 293
cells, cords of, 290
cords, 290 Herbst's corpuscles, 174, 389
technic of, 405 Hermann's solution, 24 Heterotypic mitosis, 70 Hilum of lymph-glands, 197 Histology, general, 58
special, 186
Homeotypic mitosis, 70 Honing microtome knife, 37 Horizontal cells of retina, 464
semicircular canal, 480 Horns of spinal cord, 408 Howship's lacunae, 120 Hoyer's yellow gelatin mass, 54 Huber's method of permanently mounting Golgi's preparations under coverglass, 51
Humor, aqueous, 446 Huschke's auditory teeth, 488 Huxley's layer, 390 Hyaline cartilage, 108 Hyaloid arteries, anterior, 468 posterior, 468
canal, 468
33
Hyaloid membrane of vitreous body, 467 Hydatids of Morgagni, 360 Hydrochloric acid, action of, on connective tissue, 128 as decalcifying fluid, 132 as macerating solution, 23 Hydrotropism, 61 Hymen, 359
Hypolamellar plexus, 261 Hypophysis, 423 chief cells of, 423 chromophilic cells of, 423 circulation of, 424
IMBEDDING, 27 celloidin, 30
diagram for, 32 celloidin-paraffin, 32 paraffin, 27
diagram for, 30 Immersion lens, 19
Impregnation, Cohnheim's method, 48 Cox's method 51 Gerlach's method, 48 gold chlorid method, 48 Golgi's chromsilver or chromsubli mate method, 49 gold chlorid method, 48 methods, 49 mixed method, 50 potassium bichromate and bichlorid
of mercury method, 50 potassium bichromate method, 49 rapid method, 50 slow method, 50 Kopsch's method, 52 Kiihne's method, 48 Lowit's method, 48 methods of, 47 of bile capillaries, 307 Ranvier's method, 48 silver nitrate method, 47 Indifferent fluids, 21, 22 Kronecker's, 22 physiologic saline solutions, 22 Ranvier's solution of iodin and potassium iodid, 22 Ripart and Petit's, 22 Schultze's iodized serum, 22 Indulinophile granules, technic for, 228 Inferior nasal artery of retina, 466
vein of retina, 466 papillary artery of retina, 466
vein of retina, 466 vertical semicircular canal, 480 Infiltration, 27 celloidin, 30
diagram for, 32 celloidin-paraffin, 32 paraffin, 27
diagram for, 30 Injection fluids, 53 Altman's, 55 Berlin blue, 53 carmin mass, cold, 54
INDEX.
Injection fluids, gelatin-Berlin blue, 54 gelatin-carmin, 54 silver nitrate, 55 yellow gelatin mass, 54 Injection method for demonstration of
bile capillaries, 306 of distribution of hepatic bloodvessels, 306 methods of, 53 of animals, 54 of glands, 55 of lymph-channels, 55 of lymph-spaces, 55 of lymph-vessels, 55 of organs, 55
Inner molecular layer of retina, 464 nuclear layer of retina, 459, 462 scleral sulcus, 449 Intercellular bridges, 81, 380
demonstration of, 96 spaces, 8 1 substance, 79
Interfascicular ground-substance, 105 Interglobular spaces of Czermak, 241 Interlobular arteries of kidney, 332 veins of kidney, 334
of liver, 293
Intermediate tubule of pancreas, 300 Internal auditory artery, 494 ear, 480
limiting membrane of retina, 462 Interpapillary epithelial processes, 85 Interstitial granules of Kolliker, 141 Intertubular cell-masses of pancreas, 301 Intestine, 264
absorption of fat by, 288 blood supply of, 283 large, 281
blood-vessels of mucosa of, 284 lymph-vessels of, 284 lymph supply of, 283 mucous membrane of, general structure, 264
nerves of, demonstration of, 306 muscularis mucosse of, 265 nerve supply of, 283 secretion of, 288 small, 274
axial canals of, 285 basement membrane of, 278 epthelial cells in, 275 lymphatics of, 285 lymph-nodules of, 279 mucous membrane of, 274, 277 blood-vessels of, 284 epithelium of, 274
leucocytes in, 275 lymph-nodules of, 279 villi of, 274
muscularis rnucosae of, 279 villi of, lacteals of, 285 with villi, fixation of, 305 stratum circulare of, 266 fibrosum of, 265 longitudinale of, 266 submucosa of, 265
Intestine, tunica mucosa of, 265 Intima, endothelium of, technic for, 235 Intracapsular plexuses, 429 Intracartilaginous bone, 116 Intra-epithelial glands, 88 Intrafusal muscle-fibers, 175 Intralobular duct of pancreas, 300 Intramembranous bones, 116, 122
bone-development, 122 lodo-iodid of potassium stain to demonstrate glycogen in cartilage, 131 Iris, 446, 452, 455
anterior endothelium of, 455
diaphragm, 18
nerve supply of, 456
posterior epithelium of, 455
stroma of, 455 Islands of ciliated epithelium in cervical
canal, 356 Isotropic intermediary disc, 138
JACOBSON'S organ, 499 Japanese method of fixing paraffin sections to slide, 39 Jelly, Wharton's, 100
KAES and Bechtereff's striation, 421
Karyokinesis, 64
Karyokinetic cell-division, heterotypic,
374
homeotypic, 374 Karyolysis, 74 Karyosomes, 63 Keratohyalin, 380 technic for, 403 Kidney, 323
arched collecting portion of tubules, 323
3 2 9
blood-vessels of, 332 cortical substance of, 323, 324 distal convoluted portion of tubules,
3 2 3> 3 2 9
epithelium of, demonstration of, 343 intercalated portion of tubules, 323, 329 interlobular arteries of, 332
veins of, 334 lymphatics of, 334 medullary substance of, 323 nerves of, 334, 335 pelvis of, 336
mucosa of, 337
blood-vessels of, 338 proximal convoluted portion of tubules,
3 2 3. 3 2 5
secretory processes of, 335
straight collecting tubules of, 323
technic of, 342
tubules of, demonstration of, 342
vasa afferentia of, 332 Knife, double, 21
microtome, honing of, 37
sharpening of, 37 Kolliker's interstitial granules, 141
muscle-columns, 140
INDEX.
515
Kolliker's neuropodia, 151 Kollmann's cold carmin mass, 54 Kolossow's method of demonstrating intercellular bridges, 96 Kopsch's method of impregnation, 52 Krause, end-bulbs of, 170, 388
cylindric, 172 membrane of, 137 Kronecker's fluid, 22 Kuhne's method of impregnation, 48 Kupffer's stellate cells, 295 Kytoblastema, 64
LABIUM tympanicum, 487
vestibulare, 487 Laboratory microtome, 33 Labyrinth, bony, 480
development of, 496
membranous, 480, 481 blood-vessels of, 494 technic for, 497
osseous, 480
technic for, 497 Lacrimal apparatus, 473
glands, 473
. accessory, 470
nerve supply of, 473
sac, 474
Lacteals of villi of small intestine, 285 Lacunas, Howship's, 120
of bone, 112, 113 Lamellae, 105
bone, 113
compostion of, 114 method of examining, 131
circumferential, inner, 113 outer, 113
concentric, 113
fundamental, 113
periosteal, 113 Lamina basilaris propria, 489
choriocapillaris, 452, 453
cribrosa, 448, 465
elastica interna, 218
fusca, 448
propria of oral cavity, 236 of tympanic membrane, 477
reticularis, 489, 493
spiralis membranacea, 485 ossea, 484, 486
suprachoroidea, 448, 452
vasculosa Halleri of choroid, 452 Langerhans, areas of, 301
cells of, 300 Large intestine, 281. See also Intestine,
large. Larynx, 309
cartilages of, 310
demonstration of, 322
mucous membrane of, 309
nerves of, 311
vascular supply of, 310 Lateral column, 408
mixed, 411 Ledges, terminal, 86
Lens, 446
apochromatic, 19
capsule, 468
collective, 19
crystalline, 467
anterior epithelium of, 468
fibers, 468
front, 19
immersion, 19
ocular, 19
suspensory ligament of, 467
technic of 475 Lenticular glands, 271 Leucocyte-nucleus, polymorphism of, 193 Leucocytes, 191
granulations of, 227
in epithelium of mucous membrane of small intestine, 275
method of counting, 232, 233
mononuclear, 192
motility of, 193
size of, 192
transitional, 192
with polymorphous nuclei, 192 Leucocytic granules, Ehrlich's, 192 Leydig's cells, 470 Lieberkiihn's glands, 88, 276 Ligament, suspensory, of lens, 467 Ligaments, 105
Ligamentum nuchae of ox, structure of, 106
pectinatum iridis, 454
spirale, 485, 488 Limbus spiralis, 486, 487 Lime-salts in bone, hematoxylin as stain
for, 132
isolation of, 132 Limiting membrane, external, of retina,
459, 462
internal, of retina, 462 Lines of Retzius, 239
of Schrager, 239 Lingual mucous membrane, 247 papillae of, 247
papillae, 247 Linin, 63
Liquor folliculi, 347 Liver, 289
blood-vessels of, distribution of, demonstration, 306 examination of, 343
connective tissue of, 294
interlobular veins of, 293
lobules, 289
lymphatics of, 297
nerves of, 298
demonstration of, 308
reticular fibers of, demonstration of, 308
reticulum of, 294
stellate cells of, 295
technic of, 306
tissue, technic of, 307
trabeculae of, 290 Liver-cells, examination of, 306
glycogen in, demonstration of, 306 Loop, Henle's, 323
5 i6
INDEX.
Loop, Henle's descending limb of, 327 Lo wit's method of impregnation, 48 Lugol's solution to demonstrate glycogen
in cartilage, 131 Lung alveoli, 314
blood-vessels of, 316
lobules of, 316
lymphatics of, 317
nerves of, 317
structure, units of, 316
tissue of, demonstration of, 322 Lunula, 395 Lutein, 353
cells, 353 Lymph, 186
canalicular system, 102
capillaries, 224 Lymphatic networks in endocardium, 215
system, 223 Lymph-channels, anterior, of eye, 469
injection of, 55
Lymph-follicles, germ centers of, technic for, 234
of mucosa of vermiform appendix, 281
of tongue, 251
of tonsils, 251 solitary, 197
technic for, 306 Lymph-glands, 196, 197
blood supply of, 200
capsule of, 198
hilum of, 197
lymph-sinuses of, 199 marrow, 201, 202
technic for, 233
trabeculffi of, 198
with blood-sinuses, 200 Lymph-nodules, 196
agminiited, 197
of mucosa of small intestine, 279 Lymphocytes, 191, 194
size of, 192 Lymphoid tissue, 196 Lymph-sinus, 199 Lymph-spaces, 224
injection of, 55
periaxial, 176
perichoroidal, 452 Lymph-supply of intestine, 283 Lymph-vessels, 186, 223
injection of, 55
of central nervous system, 440
of kidney, 334
of large intestine, 284
of liver, 297
of lung, 317
of mammary glands, 402
of mouth, 260
of ovary, 354
of skin, 386
of small intestine, 285
of testes, 367
of uterus, 357
MACCALLUM'S nitric acid mixture, 23
Macerating solutions, 22 alcohol, 22 caustic acid, 22
potash, 22 chromic acid, 22 hydrochloric acid, 23 MacCallum's, 23 nitric acid, 23
and chlorate of potassium, 23 sulphuric acid, 23 Maceration, methods of, 22 Macula acustica sacculi, 481
utriculi, 481 lutea, 460
region of, 460 Magenta red as stain for connective tissue,
128 Male genital organs, 361
pronucleus, 73
Mallory's differential stain for connective-tissue fibrillffi and reticulum, 128
selective neuroglia fiber-staining methods, 445 Malpighian corpuscles, 202, 203, 323, 324
pyramid, 323 Mammary gland, 400
alveoli of, epithelium of 401 lymphatics of, 402
nerves of, 402 Mantle fibers, 69 Marginal thread of spermatosome, 361
zone, 8 1
Marrow, bone-, 207. See also Bonemarrow. fat-, 207
lymph-glands, 102, 202 spaces, primary, 118
secondary, 120 Marrow-cells, 208 Martinotti's cells, 418, 419 Mast-cells, 104
granules, technic of, 228 Matrix of areolar connective tissue, 102 of nail, 394
sulcus of, 394 Mature ovum, 351
Mayer's solutions for staining mucin, 305 Median disc of Hensen, 137
membrane of Heidenhain, 137 Mediastinum testis, 363 Medullary cords, 199 rays, 323 sheath, 157 technic, 440 Benda's, 442 Pal's, 442 Weigert's, 440, 441 substance of cerebellar cortex, 416 of cerebral cortex, 419 of hair, 390 of kidney, 323 of ovary, 344 Meibomian gland, 472 Meissner's corpuscles, 170, 387 technic of, 405
INDEX.
517
Meissner's plexus, 287 Membrana capsulopupillaris, 468
praeformativa, 244
prima, 81
propria, 88, 92 of pancreas, 301 of uriniferous tubules, 330
pupillaris, 468
tectoria Cortii, 489, 493 Membrane, basement, 81, 88 of. small intestine, 278
basilar, 488
Bowman's, 449
cell, absence of, 62
Cord's, 489, 493
Descemet's, 450
endothelium of, 451 technic of, 474
elastic, anterior, of cornea, 449 posterior, of cornea, 450
external limiting, of retina, 459, 462
fenestrated, 107
glassy, of choroid, 452, 453 of hair, 391
Heidenhain's, 137
hyaloid, of vitreous body, 467
internal limiting, of retina, 462
Krause's, 137
median, of Heidenhain, 137
mucous. See also Mucous membrane.
Nasmyth's, 238
nuclear, 63
of central nervous system, 436
oral mucous, fixation of, 303
otolithic, 483
peridental, 242
pigment, of eye, 446, 447, 457
Reissner's, 485, 489
rudder, of spermatosome, 361
tympanic, 476. See also Tympanic membrane.
undulating, of spermatosome, 361
vestibular (Reissner's), 485, 489
vitreous, 452, 453
Meninges of central nervous system, 436 Menisci, tactile, 387 technic of, 405 Merkel's terminal disc, 139 Mesameboid cells, 80 Mesenchymatous tissue, 97 Mesenchyme, 80 Mesoderm, 58, 79
cells of, 80 Mesothelial cells, 80
and endothelial cells, method of
studying relations, 95 Mesothelium, 80, 92 Metakinesis, 68 Metaphases, 65, 68 Methylene-blue stain, Ehrlich's, for
nervous tissues, 182 for nerve-fibers, 184 Methyl-green as stain, 44 Metschnikoff's phagocytes, 60 Meyer's method of staining nervefibers, 184
Microcentrum, 191
Microscope and its accessories, 17
coarse adjustment of, 18
compound, 1 7
description of, 17
fine adjustment of, 18
parts of, 17
simple, 17 Microscopic preparation, 21
preparations of undecalcified bone, 131
technic, introduction to, 17 Microtome, 32
knife, honing' of, 37 sharpening of, 37
laboratory, 33
Minot automatic precision, 33, 34 rotary, 34, 35
precision, 33
rocking, 33
rotary, 35
sliding, 33
cutting celloidin sections with, 36
paraffin sections with, 35 freezing apparatus for, 36 Middle ear, 478
technic for, 497 Migratory cells, 103, 104, 193 Milk, 402
secretion, 401 Minot automatic precision microtome
33. 34
rotary microtome, 34, 35 Mitochondria, 60 Mitosis, 64
demonstration of, 75 heterotypic, 70 homeotypic, 70
Mitotic cell-division of fertilized whitefish eggs, 66, 67 ten stages of, 65 Mitral cells, 421
of olfactory bulb, 42^ Mixed gland, 258
lateral column, 411 Modified sweat-glands, 398 Modiolus, 484
Molecular layer, inner, of retina, 464 of cerebellar cortex, 413 of cerebral cortex, 417 of olfactory bulb, 421 outer, of retina, 45, 462 movement of cells, 61 Moll's glands, 398, 470 Monaster, 68
Mono nuclear leucocytes, 192 Monostratified cells of retina, 464 Montgomery's glands, 402 Morgagni, hydatids of, 360 Morula mass, 79
Mossy fibers of cerebellar cortex, 416 Mother cell, 374 nucleus, 64 skein, 67
Motor end-plate, 163 fibers, 162 nerve-endings, 162
S i8
INDEX.
Motor nerve-endings, staining of, 182 neurones. 153 peripheral, 162
diagram of, 163 Mounting, 21, 52 Mouth, glands of, small, 259
lymphatics of, 260 Muchematein, 305 Mucicarmin, 305 Mucin, demonstration of, 304, 305
staining of, 305 Mucous connective tissue, ice gland, 255
layer of tympanic membrane, 478 membrane, gastric, 266
intestinal, general structure of, 264 nerves of, demonstration of, 306 nasal, technic of, 500 of Eustachian tube, 479 of Fallopian tubes, 354 of larynx, 309 of oral cavity, 236 of pelvis of kidney, 337
blood-vessels of, 338 of small intestine, 274, 277 blood-vessels of, 284 epithelium of, 274
leucocytes in, 275 lymph-nodules of, 279 villi of, 274
of stomach, fixation of, 305 of tongue, 247 of uterus, 355 of vagina, 358
epithelium of, 358 of vermiform appendix, lymphfollicles in, 281 oral, fixation of, 303 Mucus-secreting cell, 87 Miiller's fibers, 454
of retina, 462 fluid, 26 Multicellular glands, 88
classification, 91 Muscle and tendon, relation of, method of
studying, 148 ciliary, 454 dilator, of pupil, 455 heart, 145
fibers of, MacCallum's nitric acid
mixture for isolating, 23 motor nerve-supply of, 166 nonstriated, motor nerve-supply of,
1 66
red, 141
sphincter, of pupil, 455 striated, nerve-endings in, Sihler's
method of demonstrating, 184 white, 141 Muscle-cells, cardiac, demonstration of,
148
nonstriated, 134 of fibers of Purkinje, 147 Muscle-columns of Kolliker, 140 Muscle-fibers, intrafusal, 175
nonstriated, demonstration of, 148
Muscle-fibers, striated, technic of, 147 striped, 136
voluntary, development of, 144 Muscular coat of Fallopian tubes, 355 of uterus, 356 of vagina, 359 tissue, 134
destruction of, 144 development of, 144 heart, development of, 146 nerve-fibers ending in, 162 striated, blood-vessels in, 143 technic of, 147
Muscularis mucosae of intestine 265 of small intestine, 279 of stomach, 271 Musculus ciliaris Riolani, 471 orbicularis oculi, 471 palpebralis superior, 472 Myelin sheath, 157 Myelocytes, 208 Myeloplaxes, 209 Myoblasts, 144 Myocardium, 213
NAIL, 394 bed, 394
sulcus of, 394 body of, 394 lunula of, 395 matrix, 394
sulcus of, 394 root, 394 walls, 394 Nasal artery, inferior, of retina, 466
superior, of retina, 466 cavity, 498
blood-vessels of, 499
nerves of, 500
technic of, 500
vestibule of, 498 duct, 474
mucous membrane, technic of, 500 vein, inferior, of retina, 466
superior, of retina, 466 Nasmyth's membrane, 238 Nerve end-organs, neuromuscular, 174
neurotendinous, 1 78 Nerve-cells, 149. See also Ganglion
cell.
Nerve-endings, annulospiral, 178 flower-like, 1 78 in striated muscle, Sihler's method of
demonstrating, 184 motor, 162
staining of, 182 peripheral, 162 Ruffini's, 387 sensory, 1 66
encapsulated, 169
free, 168, 169
staining of, 182 Nerve-fibers, 157
ending in muscle tissue, 162 layer of retina, 464
INDEX.
519
Nerve-fibers, medullated, demonstration
of, 1 80 of teeth, 242
methylene-blue stain for, 184 nonmedullated, 160
demonstration of, 182 of hair follicles, 393 of utriculus, 483 Nerves, auditory, 494
in taste-buds, demonstration of, 304 of bladder, 339 of bronchi, 317 of ciliary body, 456 of cornea, 451 technic, 474 of dura mater, 437 of epidermis, technic of, 405 of heart, 215 of intestine, 283
of intestinal mucous membrane, demonstration of, 306 of iris, 456 of kidney, 334, 335 of lacrimal gland, 473 of larynx, 311 of liver, 298
demonstration of, 308 of lung, 317
of mammary glands, 402 of nasal cavity, 500 of ovary, 354 of pancreas, 302 of penis, 372 of pia mater, 439 of prostate, 370 of salivary glands 260 of sclera, 451 of skin, 387
of suprarenal glands, 342 of tongue, 252 of sweat-glands, 397 of testes, 367 of thyroid gland, 320 of trachea, 311 of ureter, 339 of uterus, 358 of vagina, 360
olfactory, staining fibers of, 182 optic, 446, 464 pilomotor, 394 supplying blood-vessels, 223 Nerve-trunk, funiculi of, 160
compound, 162 Nervous system, central, 406 blood-vessels of, 439 fibrillar elements of, Apathy's method of demonstrating, 442 lymph vessels of, 440 membranes of, 436 technic of, 440 tissue, 148
Ehrlich's methylene-blue stain for,
182
fixation of, 183 technic of, 180 tunic of eye, 446, 457
Net-knots, 63
Networks, technic for, 235
Neura, 149
Neuraxes, 148, 151
Neurilemma, 158
Neurilemma-nuclei, 158
Neuroblasts, 148
Neurodendron, 149
Neuro-epithelial cells, 92
Neuro-epithelium, 92
Neurofibrils, Bethe's method of staining,
443 Neuroglia, 434
fibers, Benda's method of staining
445
Mallory's methods of staining, 445 staining of, 444 Neurogliar cells, 434 Neurokeratin, 157
Neuromuscular nerve end-organs, 174 Neurones, 149
cell-bodies of, 149 independence of, theory of, 156 motor, 153
peripheral, 162
diagram of, 163 relationship of, 431 sensory, peripheral, diagram of, 167 Neuroplasm, 157 Neuropodia, 151
Neurotendinous nerve end-organ, 178 Neutrophile granules, 193
technic for, 228 mixture Ehrlich's, 229 Nitric acid and chlorate of potassium as
macerating solution, 23 aqueous solution, as decalcifying
fluid, 133
as fixing solution, 26 as macerating solution, 23
MacCallum's, 23 Nodes of Ranvier, 158
demonstration of, 180 Nodules, 197 cortical, 198 lymph-, 196 agminated, 197
of mucosa of small intestine, 279 secondary, 197
terminal, of spermatosome, 361 Normoblasts, 208 Nuclear division, 64
layer, inner, of retina, 459, 462 membrane, 63 stains, 41 Nuclein, 63 Nucleolus, 58
true, 63 Nucleus, 58, 62
achromatic portion of, 63
chromatoid accessory, of Benda, 377
contents of, 62
daughter, 64
direct fragmentation of, 71
dorsalis, 408
gray, central, of cerebellar cortex, 416
520
INDEX.
Nucleus, leucocyte-, polymorphism of,
193
mother, 64 of spermatid, 377 resting, 63 segmentation, 7 1 sole, 163 telolemma, 163 Nuel's space, 492
OCULAR lens, 19 Odontoblasts, 240, 241, 244 Odontoclasts, 247 Olfactory bulb, 421
glomerular layer of, 421 granular layer of, 421 mitral cells of, 421 molecular layer of, 421 peripheral fibers of, 421 cells, 498 hairs, 499 region, 498
epithelium of, 498 nerve, fibers of, staining of, 182 Oocytes, 350 Optic cup, 447 nerve, 446, 464
blood-vessels of, 465 papilla, 460
region of, 460 stalks, 446 vesicles, primary, 446
secondary, 447 Ora serrata, 461 Oral cavity, 235 glands of, 253 mucous membrane of, 236
fixation of, 303 submucosa of, 236 Orbiculus ciliaris, 453 Orcein as stain for connective tissue, 128 Osmic acid as fixative for cartilage, 130 as fixing solution, 24 as stain for adipose tissue, 130 Osseous labyrinth, 480 Ossicles, auditory, 478 Ossification, centers of, 116 groove, 121 of cartilage, in ridge, 121 Osteoblasts, 118 Osteoclasts, 120 Otolithic membrane, 483 Otoliths, 483 Outer fiber layer of retina, 461
molecular layer of retina, 459, 462 Ovarian tissue, fixation of, 378 Ovary, 344
antrum of, 347 blood-vessels of, 354 cortex of, 344 germinal epithelium of, 345 lymphatics of, 354 medullary substance of, 344 nerves of, 354
Ovary, stratum granulosum of, 345
stroma of, 344
technic of, 378 Ovula Nabothi, 356 Ovum, 71, ^44
changes in, during development, 350
mature, 351
primitive, '345, 350
ripe, 350
technic for, 378
vacuole of, 344 Oxychromatin granules, 63
PACCHIONIAN bodies, 438 Pacinian corpuscles, 388
technic of, 405 Pal's method for demonstration of
medullary sheath, 442 Pancreas, 298
blood-vessels of, 302
cells of, inner and outer zones, methods
of differentiating, 308 intermediate tubule of, 300 intertubular cell-masses of, 301 intralobular duct of, 300 membrana propria of, 301 nerves of, 302 technic of, 308 zymogen granules in, demonstration of,
308
Pancreatic duct, 298 Panniculus adiposus, 384 Papilla, 84
circumvallate, 249 dentinal, 243 filiform, 248 foliate, 249 fungiform, 248 hair, 389 lingual, 247 optic, 460
region of, 460 spiralis cochlea, 481 tactile, 383 vascular, 383 Papillary artery, inferior, of retina, 466
superior, of retina, 466 vein, inferior, of retina, 466
superior, of retina, 466 Paracarmin as stain, 42
in bulk, 46 Paradidymis, 367 Paraffin imbedding, 27
diagram for, 30 infiltration, 27
diagram for, 30 removal of, 40 sections, cutting of, with sliding
microtome, 35
dextrin method of fixing, 40 distilled water for fixing of, to slide,
39 fixing of large numbers to cover-slips,
39
INDEX.
521
Paraffin sections, glycerin-albumen for
fixing of, to slide, 38 Japanese method of fixing to slide, 39 Paralinin, 63 Paranuclein, 63 Paraplasm, 60 Parareticular cells, 464 Parathyroid glands, 321 Paroophoron, 360 Parotid gland, 255 Pars ciliaris retinae, 453, 461
iridica retinas, 461
papillaris, 382
reticularis, 382
Partsch's cochineal solution, 42 Pellicula, 62 Pelvis of kidney, 336 mucosa of, 337
blood-vessels of, 338
renal, 336 Penis, 370
erectile tissue of, 371
nerves of, 372 Pepsin, effect of, on connective tissue,
128
Peptic glands, 268 Perforating fibers of cornea, 450 Periaxial lymph-space, 176 Pericardium, 214 Pericellular plexuses, 428 Perichondrium, 109 Perichoroidal lymph-spaces, 452 Peridental membrane, 242 Perilymph of cochlea, 496 Perilymphatic spaces, 224 Perimysium, 143 Perineurium, 161 Periosteal lamellae, 113 Periosteum, 112
alveolar, 242
future, 116 Peripheral fibers of olfactory bulb, 421
motor neurones, 162 diagram of, 163
nerve terminations, 162
sensory neurone, diagram of, 167 Peritendineum, 105 Perivascular spaces, 224 Petit's canal, 467 Petit and Ripart's solution, 22 Peyer's patches, 265 technic for, 306 Pfliiger's egg tubes, 345 Phagocytes, 193, 194
Metschnikoff's, 60 Phalangeal plate, 491, 492
process, 491 Pharyngeal tonsils, 252 Pharynx, 262
Physiologic excavation of retina, 460 Pia intima, 438
mater, 438
nerves of, 439 Pial funnels, 439 Picric acid as fixing solution, 25 as stain, 45
Picric acid for fixing cells, 75 Picric-nitric acid as a fixing solution,
25 Picric-osmic-acetic acid solution as fixing
fluid, 25 Picric-sublimate-osmic solution as fixing
fluid, 25 Picrocarmin as stain for connective
tissue in cartilage, 131 for elastic fibers in cartilage, 131
of Ranvier, 44
of Weigert, 45 Picrosulphuric acid as fixing solution,
25 Pigment, 97
cells, 77, 104
membrane of eye, 446, 447, 457
of cells, 6 1
of skin, 384
technic of, 404 Pillar cells, 490 heads of, 490 inner, 490 outer, 490
Pilomotor nerves, 394 Pineal gland, 422
Pituitary body, 423. See also Hypophysis. Plasma, blood, 187
cells, 104
Plate, phalangeal, 491, 492 Platelets, blood, fixation of, 227 Plates, technic for, 235 Pleura, visceral and parietal layer of, 319 Plexus, choroid, 439
epilamellar, 261, 397
ground, of cornea, 451
Heller's, 283
hypolamellar, 261
intracapsular, 429
myentericus, 286
of Auerbach, 286
of Meissner, 287
pericellular, 428
subepithelial, of cornea, 451
superficial, of cornea, 451 Plica? palmataj, 356
semilunares, 282, 473
sigmoideae, 266
transversales recti, 282 Plural staining, 44 Plurifunicular cells, 408 Polar body, 72
field, 70
rays, 68
Polarity of cells, 81
Polygonal cells of cerebral cortex, 417 Polykaryocyte, 193
Polymorphism of leucocyte-nucleus, 193 Polymorphous cells of cerebral cortex,
418
Polynuclear cells, 70 Polystratified cells of retina, 464 Portal vein, 292 Posterior hyaloid arteries, 468
vertical semicircular canal, 480
522
INDEX.
Potash, caustic, as macerating solution,
22
Potassium bichromate and formalin as fixing fluid, 27
chlorate of, nitric acid and, as macerating solution, 23
hydrate, action of, on connective
tissue, 128 Precapillary arteries, 218
veins, 220
Precision microtome, 33 Prepuce, 372 Primary blastodermic layers, 79
egg tubes of Pfliiger, 345
germ layers, 79
marrow spaces, 118
optic vesicles, 446
tendon bundles, 105 Primitive ova, 345, 350
seminal cells, 372 Primordial ova, 345 Prisms, enamel, 238 Projection fibers of cerebral cortex, 419 Prominentia spiralis, 488 Pronucleus, female, 74
male, 73
Prophases, 64, 66 Prostate, 368
blood-vessels of, 370
concretions of, 370
corpora amylacea of, 370
nerves of, 370
secretion of, 370 Prostatic bodies, 370 Protoplasm, 58, 59
of spermatids, chromatoid accessory
nucleus of, 377 sphere substance of, 376 Protoplasmic currents, 75
stains, 41 Protozoa, 58 Pseudopodia, 60 Pulp cords, 204
splenic, structure of, 205
tooth-, 241 Pupil, dilator muscle of, 455
sphincter muscle of, 455 Purkinje's cells, 153
of cerebellar cortex, 415
fibers, 213
isolated, demonstration of, 148 muscle-cells of, 147
vesicle, 344 Purpurin, alkaline, as stain for calcium
carbonate in bone, 132 Pyloric glands, 269 Pyramidal cells of cerebral cortex, 153 large, of cerebral cortex, 417 small, of cerebral cortex, 417
columns, crossed, 411
tract, direct, 411 Pyramids of Ferrein, 324
of Malpighian, 323
QUINTUPLE hydroquinon developer, 51
RABL'S hematoxylin-safranin, 46
solutions, 25 Rami cochleares, 494
vestibulares, 494
Ramon y Cajal's technic for retina, 475
Ranvier's crosses, demonstration of, 180
method for examination of connective
tissue, 126
of demonstrating glycogen in livercells, 306
spaces in bone, 132 of impregnation, 48 nodes, 158
demonstration of, 180 picrocarmin, 44 solution of iodin and potassium iodid,
22 Recessus camerae posterioris, 467
cochleae, 496 Rectum, 281 Red bone-marrow, 207
muscles, 141 Red-blood corpuscles, 187. See also
Erythrocytes .
Reissner's membrane, 485, 489 Remak's fibers, 160
demonstration of, 182 Renal artery, 332 lobes, 323 pelvis, 336
Renflement biconique, 158 Respiration, organs of, 309
technic of, 322 Respiratory bronchioles, 313
elastic fibers, demonstration of, 322 epithelium, 315
examination of, 322 region, 498 Resting nucleus, 63 Rete testis, 363
canals of, 365 Retia mirabilia, 222
_ arterial, 333 _ Reticular connective tissue, 100
cells of, 100
fibers of liver, demonstration of, 308 tissue, demonstration of, 234 Reticulum of liver, 294 Retina, 446, 447, 457 arteries of, 466 blood-vessels of, 465 central artery of, 465
vein of, 465 cone-fibers of, 459 external limiting membrane of, 459,
462
fiber-baskets of, 462 ganglion-cell layer of, 459, 464 inferior nasal artery of, 466
vein of, 466 papillary vein of, 466 inner molecular layer of, 464 nuclear layer of, 459, 462 internal limiting membrane of, 462 macula lutea of, 460 Muller's fibers of, 462
INDEX.
523
Retina, nerve-fiber layer of, 464
optic papilla of, 460
or a serrata of, 461
outer fiber layer of, 461
molecular layer of, 459, 462
pars ciliaris retinae, 461 iridica retinae, 461
physiologic excavation of, 460
relation of elements of, to one another, 462
rod-fibers of, 458
superior nasal artery of, 466
vein of, 466 papillary artery of, 466 vein of, 466
technic of, 475 Retinaculae cutis, 384 Retzius, end-piece of, 361
lines of, 239 Ring, contraction-, 158 Ripart and Petit' s solution, 22 Ripe ovum, 350 Rocking microtome, 33 Rod-fibers of retina, 458 Rod-visual cells, 458
bipolar cells of, 463 Rolando's gelatinous substance, 408 Root-sheaths of hair, 389. See also
Hair, root-sheaths of. Rose's carmin-bleu de Lyon, 45 Rouleaux, 187
Rudder membrane of spermatosome, 361 Ruffini end-organ, 388
SABIN'S modification of Mallory's differential stain for connective-tissue fibrillse and reticulum, 129
Sacculus, 481, 482 ventral, 496
Saccus endolymphaticus, 481, 496
Safranin as stain, 44
Salivary glands, 253, 255 blood supply of, 259 nerve supply of, 260
Salts, lime-, in bone, hematoxylin as
stain for, 132 isolation of, 132
Sarcolemma, 135, 137
Sarcolytes, 144
Sarcomeres, 138
Sarcoplasm, 135, 137
Sarcous elements, 141
Scala media, 485 tympani, 485 vestibuli, 485
Schachowa's spiral segment, 327
Schlemm's canal, 448
Schmidt-Lantermann-Kuhnt's segments,
157
Schmorl's method of staining bone corpuscles, 133
Schrager's lines, 239
Schron's granule, 344
Schultze's iodized serum, 22
Schwann, sheath of, 158
Sclera, 446, 448
blood-vessels of 449
nerve supply of, 451
technic of, 475 Scleral conjunctiva, 448
sulcus, inner, 449 Sebaceous glands, 398 Secondary marrow spaces, 120
optic vesicle, 447
tendon bundles, 105 Secretion, milk, 401
of intestine, 288
of prostate, 370
process of, 92
vacuoles, 291
Secretory processes of kidney, 335 Sectioning, 32 Sections, 2 1
staining of, 41
Sectionwork, appropriate stains for, 235 Segmentation nucleus, 71 Segments, Schmidt-Lantermann-Kuhnt's,
157
spiral, of Schachowa, 327 Selective stains, 41 Semicircular canal, 483
anterior superior vertical, 480 external, 480 horizontal, 480
posterior inferior vertical, 480 Semilunar fold, 484 Seminal cells, primitive, 372 fluid, examination of, 378 vesicles, 368 Sense cells, 81 Sensory nerve-endings, 166 encapsulated, 169 free, 168, 169 staining of, 182
neurone, peripheral, diagram of, 167 Septa renis, 324 Septum posticum, 438 Serous cavities, 224
gland, 255 Sertoli's cells, 364 Sexual cells, fertilization of, 71 male, development of, 72 matured, 7 1
Sharpening microtome knife, 37 Sharpey, fibers of, 115
method of isolating, 134 Sheath, axial, 176 Henle's, 162 medullary, 157 technic, 440 Benda's, 442 Pal's, 442 Weigert's, 440, 441 myelin, 157
of axial thread of spermatosome, 361 of Schwann, 158 Shedding hair, 393
Sihler's method of demonstrating nerveendings in striated muscle, 184 Silver nitrate as injection fluid, 55 method of impregnation, 47
524
INDEX.
Simple epithelium, 82. See also Epithelium, simple.
microscopes, 17 Sinus, blood, 222
lactiferus, 400
lymph-, 199
pocularis, 370 Sinuses, 222 ,
Sinusoids, 221 Skein, mother, 67 Skin, 379
and appendages, 379 technic of, 403
glands of, 396
lymph-vessels of, 386
nerves of, 387
pigment of, 384 technic for, 404
structure of, technic for, 404
true, 379
vascular system of, 386 Slide digestion for connective tissue, 129 Slides, 20
Sliding microtome, 33. See also Microtome, sliding. Small intestine, 274. See also Intestine,
small.
Smell, organ of, 498 Sole nuclei, 163
plate, granular, 163 Somatic cell, 71
Specimens, permanent, preparation of, 52 Spermatids, 72, 374
develoment of, into spermatosomes,
374, 37
nucleus of, 377
protoplasm of, chromatoid accessory
nucleus of, 377 sphere substance of, 376 Spermatoblast, 376 Spermatocytes, 70, 72
of first order, 374
of second degree, 374
of third degree, 374 Spermatogenesis, 372
schematic diagrams of, 373
technic of, 378 Spermatogones, 72 Spermatogonia, 372 Spermatosome, 361
accessory thread of, 361
axial thread of, 361 sheath of, 361
development of, from spermatids 374 376
flagellum of, 361
head of, 361
marginal thread of, 361
middle piece of, 361
rudder membrane of, 361
tail of, 361
terminal nodule of, 361
undulating membrane of, 361 Spermatozoa, 60, 71, 73 Spermatozoon, 361. See also Spermatosome.
Sphere substance of protoplasm of
spermatids, 376 Sphincter muscle of pupil, 455 Spider cells, 435 Spinal cord, 406
anterior median fissure of, 406 commissures of, 412 gray substance of, 406, 409 horns of, 408
posterior median septum of, 406 white substance of, 406, 409 ganglia, 424
ganglion cell of Dogiel, 426 Spindle, achromatic, 68
central, 68 Spindle-shaped cells of cerebral cortex,
417 Spiral ganglion of cochlea, 494
organ of Corti, 489
segment of Schachowa, 327 Spirem, 67 Spleen, 202
blood supply of, 203
lobules, 204
diagram of, 205
trabeculae of, 203 Splenic pulp, structure of, 206
tissue, demonstration of, 234 Splenolymph glands, 201 Spongioblasts, 434
diffuse, 464
stratum, 464 Spongioplasm, 60, 274 Spot, Wagner's, 344 Staining, 41
blood-cells, 227
blood films, Wright's method, 229
bone corpuscles, Schmorl's method,
133 double, 44
of cells, 76
fibers of olfactory nerve, 182 in bulk, 46
diagram for, 47 in sections, diagram for, 47 motor nerve-endings, 182 neurofibrils and Golgi-nets, Bethe's
method, 443 neuroglia, 444
fibers, Benda's method, 445
Mallory's methods, 445 plural, 44 section, 41
sensory nerve-endings, 182 Stains, 41 acid, 41
fuchsin-picric acid solution, van Gieson's, 45
hemalum, 43
alkaline purpurin, for calcium carbonate in bone, 132 alum-carmin, 42
for bulk, 46 anilin, 44 basic, 41 Biondi-Heidenhain triple, 46
INDEX.
525
Stains, Bismarck brown, 44 borax-carmin, alcoholic, 41 for bulk, 46
aqueous, 41 carmin, 41
carmin-bleu de Lyon, 45 coal-tar, 44
Czocor's cochineal solution, 42 differential, for connective-tissue fi brillae and reticulum, 128 Ehrlich's methylene-blue, for nervous
tissues, 182
eosin, for blood-cells, 227 for adipose tissue, 130 for canalicular system in cartilage, 131 for mucin, 305 for sectionwork, 235 fuchsin-resorcin elastic fibers, 128 gold chlorid, for capsules of cartilage,
J3 1
Heidenhain's iron, for bulk, 46 hemalum, 43
acid, 43
for bulk, 46
hematoxylin, Bohmer's, 42 for bulk, 46
Delafield's, 43
Ehrlich's, 43
for nuclei and granules, 228
for lime-salts in bone, 132
Friedlander's glycerin-, 43 hematoxylin-eosin, 45 hematoxylin-safranin, 46 hematoxylon, 42
Heidenhain's iron, 43 iodo-iodid of potassium, to demonstrate
glycogen in cartilage, 131 magenta red, for connective tissue, 128 methylene-blue, for nerve-fibers, 184 methyl-green, 44 nuclear, 41
orcein, for connective tissue, 128 paracarmin, 42
for bulk, 46
Partsch's cochineal solution, 42 picric acid, 45 picrocarmin, Ranvier's, 44
Weigert's, 45 protoplasmic, 4 1 safranin, 44 selective, 41 Sudan III, for fat, 130 triple, 46
Stars, daughter, 374 Stellate cells of cerebellar cortex, 415
large, of cerebellar cortex, 416
of cerebral cortex, 417
of liver, 295 Stellular vasculosae, 453 Steno's ducts, 253 Stomach, 264, 266 blood-vessels of, 284 crypts of, 266 epithelium and secretory cells of,
changes in, during secretion, 271 foveolae of, 266
Stomach, glands of, 267 cardiac, 267 fundus, 268 pyloric, 269
mucous membrane of, 266 fixation of, 305
muscularis mucosae of, 271 Stomach-pits, 266 Straight tubules of testes, 363 Stratified epithelium, 83. See also Epithelium, stratified. Stratum circulare, 477 of intestine, 266
corneum, 379, 381
fibrosum of intestine, 265
germinativum, 379
granulosum, 379 of ovary, 347
longitudinale of intestine, 266
lucidum, 381 technic for, 403
Malpighii, 379 technic of, 403
proprium of oral cavity, 236
radiatum, 477
spongioblasts, 464
submucosum of oral cavity, 236 Stria vascularis, 488 Striated muscle, nerve-endings in, Sihler's method of demonstrating, 184
muscle-fibers, technic of, 147
muscular tissue, blood-vessels in, 143 Striation of Baillarger, 421
of Bechtereff and Kaes, 421
of iris, 455
of ovary, 344
of red blood-corpuscles, 187 Subarachnoid space, 437 Subdural space, 437 Subepithelial plexus of cornea, 451 Sublingual gland, 255 Submaxillary gland, 258 Submucosa of intestine, 265
of oral cavity, 236
of urethra, 372 Substantia propria of cornea, 449
technic for, 474 Succus prostaticus, 370 Sudan III as stain for fat, 130 Sudoriparous glands, 396. See also Sweatglands. Sulcus of matrix of nail, 394
spiralis internus, 487 Sulphuric acid as macerating solution, 23 Superficial plexus of cornea, 45 1 Superior nasal artery of retina, 466 vein of retina, 466
papillary artery of retina, 466
vein of retina, 466 Suprarenal capsule, demonstration of,
343 glands, 339
blood-vessels of, 341
nerves of, 342
Suspensory ligament of lens, 467 Sustentacular cells, 92, 250, 372, 483
526
INDEX.
Sustentacular fiber 492 Sweat-glands, 396
capillaries of, 397
coiled portion of, 396
modified, 398
nerves of, 397 Sympathetic ganglia, 427 Syncytium, 97
development and differentiation, 98
TACTILE corpuscles, Meissner's, 387 technic of, 405
menisci, 387 technic of, 405
papilla?, 383 Tsenise coli, 266
semilunares, 282
Tannic acid, effect on red blood-corpuscles, 189 Tapetum cellulosum, 453
fibrosum 453 Tarsal gland, 472 Taste-buds, 249
nerves in, demonstration of, 304
technic for, 303 Taste-pore, 250 Teasing, 2 1 Teeth, 238
adult, structure of. 238
auditory, 488
blood-vessels of, 242
development of, 243 method of studying, 303
medullated nerve-fibers of, 242
pulp of, 241
technic for, 303 Teichmann's crystals, 188
method of obtaining, 230 Tela submucosa, 236 Tellyesnicky's fluid, 26 Telodendria, 150, 162 Telolemma nuclei, 163 Telophases, 65, 70
Temperature, high, effect on tissues, 29 Temporal artery, inferior, of retina, 466 superior, of retina, 466
vein, inferior, of retina, 466
superior of retina, 466 Tendon, 105
and muscle, relation of, method of studying, 148
bundles, primary, 105 secondary, 105
cells from tail of rat, 107
fasciculi, 105 Tenon's capsule, 448 Terminal bronchioles, 314, 315
fibers of cerebral cotex, 420
ledges, 86
nodule of spermatosome, 361 Testes, 362
blood-vessels of, 367
convoluted tubules of, 363
examination of, 378
lymph-vessels of, 367
Tests, nerves of, 367 straight tubules of, 363 vasa efferentia of, 363, 365 Theca folliculi, 347 Third eyelid, 473 Thoma's ampullae, 204
Zwischenstiick, 204 Thoma-Zeiss hemocytometer, 232 Thread-granules, 60 Thrombocytes, 194 Thymus gland, 210
blood supply of, 212 Thyroid gland, 319
acini of, chief cells of, 320
colloid cells of, 320 blood supply of, 320 demonstration of, 322 nerves of, 320 granules, 149 Tissue, 79 adipose, 107
stain for, 130 connective, 96. See also Connective
tissue.
effect of high temperature on, 29 elastic, effect of trypsin digestion on,
127
method of obtaining, 127 epithelial, 80 erectile, 371 fibrous, elastic, 106 liver, technic of, 307 lymphoid, 196 mesenchymatous, 97 muscular, 134
destruction of, 144 development of, 144 heart, development of, 146 nerve-fibers ending in, 162 striated, blood-vessels in, 143 technic of, 147 nervous, 148
Ehrlich's methylene-blue stain for,
182
fixation of, 183 technic of, 180 ovarian, fixation of, 378 pulmonary, demonstration of, 322 reticular, demonstration of, 234 splenic, demonstration of, 234 Toison's fluid for diluting blood, 232 Tomes' granular layer, 246
processes, 244 Tongue, 247
lymph -follicles of, 251 mucous membrane of, 247 nerve supply of, 252 papillae of, 247 Tonsils, lymph-follicles of, 251
pharyngeal, 251 Trabeculae of liver, 290 of lymph-glands, 198 of spleen, 203 Trachea, 310
demonstration of, 322 nerves of, 311
INDEX.
527
Transitional epithelium, 85
leucocytes, 192 Triple stains, 46 Trophoplasts, 385 Trypsin digestion, effect on connective
and elastic tissues, 127 Tubular glands, 89 coiled, 90
compound branched, 90 reticulated, 90 simple branched, 90 Tubules, convoluted, of testes, 363 dentinal, 240
intermediate, of pancreas, 300 of kidney, demonstration of, 342 straight collecting, of kidney, 323
of testes, 363 uriniferous, 323
membrana propria of, 330 Tubuli recti, 363 Tubulo-alveolar gland, 90 Tunica albuginea, 92, 344, 362 dartos, 384 externa of eye, 446 fibrosa of eye, 446, 448 interna of eye, 446, 457 mucosa of intestine, 265 propria of oral cavity, 236 sclerotica, 446, 448. See also Sclera. vaginalis, 362 vasculosa, 362
of eye, 446, 452 Tunics of eye, 446 Tunnel-fibers, 494 Tympanic investing layer, 489 membrane, 476
cutaneous layer of, 476
epidermis of, 476 lamina propria of, 477 mucous layer of, 478 Tympanum, 478 Tyson, glands of, 372
UNDECALCIFIED bone, microscopic preparations of, 131 Undulating membrane of spermatosome,
361
Unicellular glands, 87 Unna's orcein stain for connective tissue,
128 Ureter, 336
nerves of, 339
technic of, 343 Urethra, epithelium of, 371
submucosa of, 372 Urinary organs, 323 Uriniferous tubules, 323
membrana propria of, 330 Uterus, 355
blood supply of, 357
lymphatics of, 357
mucous membrane of, 355
muscular coat of, 356
nerves of, 358 Utriculosaccular duct, 481
Utriculus, 481, 482 dorsal, 496 nerve-fibers of, 483 wall of, 482
VACUOLE of ovum, 344 Vacuoles, 61
secretion, 291 Vagina, 358
mucous membrane of, 358 epithelium of, 358
muscular coat of, 359
nerves of, 360
vestibule of, epithelium of, 360 Valves, auriculoventricular, of heart, 213
of veins, 220
Valvulas conniventes, 265, 274 Van Gieson's acid fuchsin-picric acid
solution, 45 Vas aberrans Halleri, 366
deferens, 367
epididymidis, 364, 366
spirale, 489 Vasa afferentia, 197 of kidney, 332
cfferentia, 197
of testes, 363, 365
recta spuria, 334 Vascular canals, 112
papillae, 383
supply of larynx, 310
system, 213 of skin, 386
tunic of eye, 446, 452 Vater-Pacinian corpuscles, 1 73
distribution of, 174 Veins, 219
central, of retina, 465
interlobular, of kidney, 334 of liver, 293
nasal, inferior, of retina, 466 superior, of retina, 466
papillary, inferior, of retina, 466 superior, of retina, 466
portal, 292
precapillary, 220
small, 220
temporal, inferior, of retina, 466 superior, of retina, 466
valves of, 220 Venae arciformes, 334
stellatae, 334
vorticosae, 452 Ventral sacculus, 496 Ventrolateral column, 408 Ventromesial column, 408 Venulae rectae, 334
Vermiform appendix, mucosa of, lymphfollicles of, 281 Vesicles, germinal, 71
optic, primary, 446 secondary, 447
Purkinje's, 344
seminal, 368
(Reissner's), 485, 489
INDEX.
Vestibule of ear, 480
of nasal cavity, 498
of vagina, epithelium of, 360 Villi of mucous membrane of small intestine, 274
of small intestine, lacteals of, 285 Virchow's bone corpuscles, method of
isolating, 134 Visual cells, 458 Vitreous body, 446, 467
hyaloid membrane of, 467
membrane, 452, 453 Volkmann's canals, 115 vom Rath's solutions, 25 von Ebner's method of decalcification,
133 von Koch's technic for bone, 132
WAGNER'S spot, 344
Wandering cells, 60, 103, 104
Water, distilled, for fixing paraffin
sections to slide, 39 effect on red blood-corpuscles, 188 Wax plates, 56
apparatus for making, 56 reconstruction by, 55 Bern's method, 56 cutting out parts to be reconstructed, and completing model,
J 57.
drawing apparatus, 56 serial sections, 56
Weigert's fuchsin-resorcin elastic fibers stain, 128
Weigert's methods for demonstration of medullary sheath, 440, 441
picrocarmin, 45 Wharton's ducts, 253, 254
jelly, 100
White blood-corpuscles, 191. See also Leucocytes.
fibers, 99
fibrocartilage, no
muscles, 141
rami communicantes, 429 fibers, 429, 456
substance of spinal cord, 406, 409 Wirsungian duct, 298 Wolffian duct, 360 Wright's method of staining blood
films, 229 Wrisberg, cartilages of, 310
YELLOW bone-marrow, 207, 210 gelatin mass as injection fluid, 54
ZENKER'S fluid, 26 Zinn's arterial circle, 465
zonule, 467
Zona pellucida, origin of, 350 Zone, boundary, of choroid, 453
marginal, 8 1 Zonula ciliaris, 446, 467 Zonule of Zinn, 467 Zymogen, 255
granules in pancreas, demonstrating, 308
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" I have seen no plates which impress me as so truly representing histologic appearances as do these. The book is a valuable one."
Howell's Physiology
A Text=Book of Physiology. By WILLIAM H. HOWELL, PH.D., M. D., Professor of Physiology in the Johns Hopkins University, Baltimore, Md. Octavo of 1018 pages, 306 illustrations. Cloth, $4.00 net.
THE NEW (4th) EDITION
Dr. Howell has had many years of experience as a teacher of physiology in several of the leading medical schools, and is therefore exceedingly well fitted to write a text-book on this subject. Main emphasis has been laid upon those facts and views which will be directly helpful in the practical branches of medicine. At the same time, however, sufficient consideration has been given to the experimental side of the science. The entire literature of physiology has been thoroughly digested by Dr. Howell, and the important views and conclusions introduced into his work. Illustrations have been most freely used. The Lancet, London
" This is one of the best recent text-books on physiology, and we warmly commend it to the attention of students who desire to obtain by reading a general, all-round, yet concise survey of the scope, facts, theories, and speculations that make up its subject matter."
SAUNDERS' BOOKS ON
McFar land's Pathology
A Text-Book of Pathology. By JOSEPH McFARLAND, M. D., Professor of Pathology and Bacteriology in the Medico-Chirurgical College of Philadelphia. Octavo of 856 pages, with 437 illustrations, many in colors. Cloth, $5.00 net; Half Morocco, $6.50 net.
THE NEW (2d) EDITION
You cannot successfully treat disease unless you have a practical, clinical knowledge of the pathologic changes produced by disease. For this purpose Dr. McFarland's work is well fitted. It was written with just such an end in view to furnish a ready means of acquiring a thorough training in the subject, a training such as would be of daily help in your practice. For this edition every page has been gone over most carefully, correcting, omitting the obsolete, and adding the new. Some sections have been entirely rewritten. You will find it a book well worth consulting, for it is the work of an authority.
St. Paul Medical Journal
" It is safe to say that there are few who are better qualified to give a resume 1 of the modern views on this subject than McFarland. The subject-matter is thoroughly up to date."
Boston Medical and Surgical Journal
" It contains a great mass of well-classified facts. One of the best sections is that on the special pathology of the blood."
McFarland's
Biology: Medical and General
Biology: Medical and General By JOSEPH MCFARLAND, M. D., Professor of Pathology and Bacteriology in the Medico-Chirurgical College of Phila. 1 2mo, 440 pages, 1 60 illustrations. Cloth, $1.75 net.
ILLUSTRATED
This work is both a general and medical biology. The former because it discusses the peculiar nature and reactions of living substance generally; the latter because particular emphasis is laid on those subjects of special interest and value in the study and practice of medicine. The illustrations will be found of great assistance.
Frederic P. Gorh&m, A. M., Brown University.
" I am greatly pleased with it. Perhaps the highest praise which I can give the book is to say that it more nearly approaches the course I am now giving in general biology than any other work."
BA CTERIOL OGY AND HISTOL OGY.
McFarland's Pathogenic Bacteria
The New (6th) Edition, Revised
A Text-Book Upon the Pathogenic Bacteria. By JOSEPH McFARLAND, M. D., Professor of Pathology and Bacteriology in the MedicoChirurgical College of Philadelphia, Pathologist to the Medico-Chirurgical Hospital, Philadelphia, etc. Octavo volume of 709 pages, finely illustrated. Cloth, $3.50 net
FULLY ILLUSTRATED
This book gives a concise account of the technical procedures necessary in the study of bacteriology, a brief description of the life-history of the important pathogenic bacteria, and sufficient description of the pathologic lesions accompanying the micro-organismal invasions to give an idea of the origin of symptoms and the causes of death. The illustrations are mainly reproductions of the best the world affords, and are beautifully executed. In this edition the entire work has been practically rewritten, old matter eliminated, and much new matter inserted.
H. B. Anderson, M. D.,
Professor of Pathology and Bacteriology, Trinity Medical College, Toronto.
" The book is a satisfactory one, and I shall take pleasure in recommending it to the students
of Trinity College." e
The Lancet, London
" It is excellently adapted for the medical students and practitioners for whom it is avowedly written. . . . The descriptions given are accurate and readable."
Hill's Histology and Org'anog'raphy
A Manual of Histology and Organography. By CHARLES HILL, M. D., formerly Assistant Professor of Histology and Embryology, Northwestern University, Chicago. I2mo of 468 pages, 337 illustrations. Flexible leather, $2.00 net.
THE NEW (2dJ EDITION
Dr. Hill's work is characterized by a completeness of discussion rarely met in a book of this size. Particular consideration is given the mouth and teeth.
Pennsylvania Medical Journal
" It is arranged in such a manner as to be easy of access and comprehension. To any contemplating the study of histology and organography we would commend this work."
SAUNDERS' BOOKS ON
GET A THE NEW
THE BEST /V HI C f 1 C <& II STANDARD
Illustrated Dictionary
New (6th) Edition, Entirely Reset
The American Illustrated Medical Dictionary. A new and complete dictionary of the terms used in Medicine, Surgery, Dentistry, Pharmacy, Chemistry, Veterinary Science, Nursing, and kindred branches ; with over 100 new and elaborate tables and many handsome illustrations. By W. A. NEWMAN BORLAND, M.D., Editor of " The American Pocket Medical Dictionary." Large octavo, 986 pages, bound in full flexible leather. Price, $4.50 net ; with thumb index, $5.00 net
IT DEFINES ALL THE NEW WORDS IT IS UP TO DATE
Dorland's Dictionary defines hundreds of the newest terms not defined in any other dictionary bar none. These new terms are live, active words, taken right from modern medical literature.
It gives the capitalization and pronunciation of all words. It makes a feature of the derivation or etymology of the words. In some dictionaries the etymology occupies only a secondary place, in many cases no derivation being given at all. In ' ' Dorland, ' ' practically every word is given its derivation.
In "Dorland" every word has a separate paragraph, thus making it easy to
find a word quickly.
The tables of arteries, muscles, nerves, veins etc., are of the greatest help
in assembling anatomic facts. In them are classified for quick study all the
necessary information about the various structures.
In "Dorland" every word is given its definition a definition that defines
in the fewest possible words. In some dictionaries hundreds of words are not
defined at all, referring the reader to some other source for the information he
wants at once.
Howard A. Kelly, M. D., Johns Hopkins University, Baltimore
" Dr. Dorland's dictionary is admirable. It is so well gotten up and of such convenient size. No errors have been found in my use of it."
J. Collins Warren. M. D., LL.D., F.R.C.S. (Hon.), Harvard Medical School
" I regard it as a valuable aid to my medical literary work. It is very complete and of convenient size to handle comfortably. I use it in preference to any other."
PATHOLOGY.
Stengel's Text-Book of Pathology
The New (5th) Edition
A Text-Book of Pathology. By ALFRED STENGEL, M. D., Professor of Medicine in the University of Pennsylvania. Octavo volume of 979 pages, with 400 text-illustrations, many in colors, and 7 full-page colored plates. Cloth, $5.00 net; Sheep or Half Morocco, $6.50 net.
WITH 400 TEXT-CUTS. MANY IN COLORS, AND 7 COLORED PLATES
In this work the practical application of pathologic facts to clinical medicine is considered more fully than is customary in works on pathology. While the subject of pathology is treated in the broadest way consistent with the size of the book, an effort has been made to present the subject from the point of view of the clinician. In the second part of the work the pathology of individual organs and tissues is treated systematically and quite fully under subheadings that clearly indicate the subject-matter to be found on each page. In this edition the section dealing with General Pathology has been most extensively revised, several of the important chapters having been practically rewritten. A very useful addition is an Appendix treating of th- technic of pathologic methods, giving briefly the most important methods at present in use for the study of pathology, including, however, only those methods capable of giving satisfactory results. The book will be found to maintain fully its popularity.
PERSONAL AND PRESS OPINIONS
William H. Welch. M. D..
Professor of Pathology, Johns Hopkins University, Baltimore, Md.
" I consider the work abreast of modern pathology, and useful to both students and practitioners. It presents in a concise and well-considered form the essential facts of general and special pathologic anatomy, with more than usual emphasis upon pathologic physiology."
Ludvig Hektoen, M. D..
Professor of Pathology, Rush Medical College, Chicago.
" I regard it as the most serviceable text-book for students on this subject yet written by an American author."
The Lancet, London
" This volume is intended to present the subject of pathology in as practical a form as possible, and more especially from the point of view of the 'clinical pathologist.' These subjects have been faithfully carried out, and a valuable text-book is the result. We can most favorably recommend it to our readers as a thoroughly practical work on clinical pathology."
SAUNDERS' BOOKS ON
Mallory and Wright's Pathologic Technique
New (5th) Edition, Revised
Pathologic Technique. A Practical Manual for Workers in Pathologic Histology, including Directions for the Performance of Autopsies and for Clinical Diagnosis by Laboratory Methods. By FRANK B. MALLORY, M. D., Associate Professor of Pathology, Harvard University ; and JAMES H. WRIGHT, M. D., Director of the Pathologic Laboratory, Massachusetts General Hospital. Octavo of 500 pages, with 152 illustrations. Cloth, $3.00 net.
WITH CHAPTERS ON POST-MORTEM TECHNIQUE AND AUTOPSIES
In revising the book for the new edition the authors have kept in view the needs of the laboratory worker, whether student, practitioner, or pathologist, for a practical manual of histologic and bacteriologic methods in the study of pathologic material. Many parts have been rewritten, many new methods have been added, and the number of illustrations has been considerably increased. Among the new matter are the following : Smith's staining method for encapsulated bacteria ; the antiformin method for detection and cultivation of tubercle bacilli ; Musgrave's and Clegg's method for the cultivation of amebas ; Wright's method for staining myelin sheaths in frozen sections ; Ghoreyeb's method for spirochetes ; Alzheimer's method for cytologic examination of cerebrospinal fluid ; Giemsa's new method for protozoa and bacteria in sections, and the Wassermann-Noguchi tests for syphilis.
PERSONAL AND PRESS OPINIONS
Wm. H. Welch, M. D.,
Professor of Pathology, Johns Hopkins University, Baltimore.
" I have been looking forward to the publication of this book, and I am glad to say that I find it a most useful laboratory and post-mortem guide, full of practical information and well up to date."
Boston Medical and Surgical Journal
" This manual, since its first appearance, has been recognized as the standard guide in pathological technique, and has become well-nigh indispensable to the laboratory worker."
Journal of the American Medical Association
" One of the most complete works on the subject, and one which should be in the library rf every physician who hopes to keep pace with the great advances made in pathology."
EMBRYOLOGY.
Heisler's Text-Book qf Embryology
Third Edition
A Text-Book of Embryology. By JOHN C. HEISLER, M.D., Professor of Anatomy in the Medico-Chirurgical College, Philadelphia. Octavo volume of 435 pages, with 212 illustrations, 32 of them in colors. Cloth, $3.00 net.
WITH 212 ILLUSTRATIONS, 32 IN COLORS
The fact of embryology having acquired in recent years such great interest in connection with the teaching and with the proper comprehension of human anatomy, it is of first importance to the student of medicine that a concise and yet sufficiently full text-book upon the subject be available. This new edition represents all the latest advances recently made in the science of embryology. Many portions have been entirely rewritten, and a great deal of new and important matter added. A number of new illustrations have also been introduced and these will prove very valuable. The previous editions of this work filled a gap most admirably, and this new edition will undoubtedly maintain the reputation already won. Heisler's Embryology has become a standard work.
PERSONAL AND PRESS OPINIONS
G. Carl Huber, M.D.,
Professor of Embryology at the Wistar Institute, University of Pennsylvania. " I find the second edition of ' A Text-Book of Embryology' by Dr. Heisler an improvement on the first. The figures added increase greatly the value of the work. I am again recommending it to our students."
William Wathen, M. D.,
Professor of Obstetrics, Abdominal Surgery, and Gynecology, and Dean, Kentucky School of
Medicine, Louisville, Ky,
" It is systematic, scientific, full of simplicity, and just such a work as a medical student will be able to comprehend."
Birmingham Medical Review, England
" We can most confidently recommend Dr. Heisler's book to the student of biology or medicine for his careful study, if his aim be to acquire a sound and practical acquaintance with the subject of embryology."
io SAUNDERS' BOOKS ON
Wells* Chemical Pathology
Chemical Pathology. Being a Discussion of General Pathology from the Standpoint of the Chemical Processes Involved. By H. GIDEON WELLS, PH. D., M. D., Assistant Professor of Pathology in the University of Chicago. Octavo of 549 pages. Cloth, $3.25 net.
A PRACTICAL BOOK
Dr. Wells' work is written for the physician, for those engaged in research in pathology and physiologic chemistry, and for the medical student. In the introductory chapter are discussed the chemistry and physics of the animal cell, giving the essential facts of ionization, diffusion, osmotic pressure, etc., and the relation of these facts to cellular activities. Special chapters are devoted to Diabetes and to Uric-acid Metabolism and Gout.
Wm. H. Welch. M. D.
Professor of Pathology, Johns Hopkins University.
" The work fills a real need in the English literature of a very important subject, and I shall be glad to recommend it to my students."
Lusk's Elements of Nutrition
Elements of the Science of Nutrition. By GRAHAM LUSK, PH. D., Professor of Physiology at Cornell Medical School. Octavo volume of 302 pages. Cloth, $3.00 net.
THE NEW (2d) EDITION TRANSLATED INTO GERMAN
Prof. Lusk presents the scientific foundations upon which rests our knowledge of nutrition and metabolism, both in health and in disease. There are special chapters on the metabolism of diabetes and fever, and on purin metabolism. The work will also prove valuable to students of animal dietetics at agricultural stations.
Lewellys F. Barker, M. D.
Professor of the Principles and Practice of Medicine, Johns Hopkins University. " I shall recommend it highly to my students. It is a comfort to have such a discussion of the subject in English."
HISTOLOGY. ii
Bohm, Davidoff, and Huber's Histology
A Text=Book of Human Histology. Including Microscopic Technic. By DR. A. A. BOHM and DR. M. VON DAVIDOFF, of Munich, and G. GARL HUBER, M.D., Professor of Embryology at the Wistar Institute, University of Pennsylvania. Handsome octavo of 528 pages, with 361 beautiful original illustrations. Flexible cloth, $3.50 net.
THE NEW (2d) EDITION, ENLARGED
The work of Drs. Bohm and Davidoff is well known in the German edition, and has been considered one of the most practically useful books on the subject of Human Histology. This second edition has been in great part rewritten and very much enlarged by Dr. Huber, who has also added over one hundred original illustrations. Dr. Huber's extensive additions have rendered the work the most complete students' text-book on Histology in existence.
Boston Medical and Surgical Journal
" Is unquestionably a text-book of the first rank, having been carefully written by thorough masters of the subject, and in certain directions it is much superior to any other histological manual."
DrewV
Invertebrate Zoology
A Laboratory Manual of Invertebrate Zoology. By OILMAN A. DREW, PH.D., Professor of Biology at the University of Maine. With the aid of Members of the Zoological Staff of Instructors of the Marine Biological Laboratory, Woods Holl, Mass, tamo of 200 pages. Cloth, #1.25 net.
A LABORATORY WORK
The subject is presented in a logical way, and the type method of study has been followed, as this method has been the prevailing one for many years.
Prof. Allison A. Smyth, Jr., Virginia Polytechnic Institute
" I think it is the best laboratory manual of zoology I have yet seen. The large number of forms dealt with makes the work applicable to almost any locality."
12 SAUNDERS BOOKS ON
Norris' Cardiac Pathology
Studies in Cardiac Pathology. By GEORGE W. NORRIS, M.D., Associate in Medicine at the University of Pennsylvania. Large octavo of 235 pages, with 85 superb illustrations. Cloth, $5.00 net.
SUPERB ILLUSTRATIONS
The wide interest being manifested in heart lesions makes this book particularly opportune. The illustrations are superb and are faithful reproductions of the specimens photographed. Each illustration is accompanied by a detailed description ; besides, there is ample letter press supplementing the pictures. Considerable matter of a diagnostic and therapeutic nature has been interwoven.
Boston Medical and Surgical Journal
"The illustrations are arranged in such a way as to illustrate all the common and many of the rare cardiac lesions, and the accompanying descriptive text constitutes a fairly continuous didactic treatise."
McConnell's Pathology
A Manual of Pathology. By GUTHRIE McCoNNELL,M.D., Professor of Bacteriology and Pathology at Temple University, Philadelphia. I2mo of 523 pages, with 170 illustrations. Flexible leather, $2.50 net.
NEW (2d) EDITION
Dr. McConnell has discussed his subject with a clearness and precision of style that make the work of great assistance to both student and practitioner. The illustrations have been introduced for their practical value.
New York State Journal of Medicine
" The book treats the subject of pathology with a thoroughness lacking in many works of greater pretension. The illustrations many ef them original are profuse and of exceptional excellence."
Hektoen and Riesman's Pathology
AMERICAN TEXT-BOOK OF PATHOLOGY. Edited by LUDVIG HEKTOEN, M.D., Professor of Pathology, Rush Medical College, Chicago; and DAVID RIESMAN, M.D., Professor of Clinical Medicine, Philadelphia Polyclinic. Octavo of 1245 pages, ^43 illustrations, 66 in colors. Cloth, $7.50 net ; Half Morocco, $9.00 net.
HISTOLOGY. 13
Diirck anc Hektoen's
Special Pathologic Histology
Atlas and Epitome of Special Pathologic Histology. By DR. H.
DURCK, of Munich. Edited, with additions, by LUDVIG HEKTOEN, M. D., Professor of Pathology, Rush Medical College, Chicago. In two parts. Part I. Circulatory, Respiratory, and Gastro-intestinal Tracts. 120 colored figures on 62 plates, and 158 pages of text. Part II. Liver, Urinary and Sexual Organs, Nervous System, Skin, Muscles, and Bones. 123 colored figures on 60 plates, and 192 pages of text. Per part : Cloth, $3.00 net. In Saunders' Hand- Atlas Series.
The great value of these plates is that they represent in the exact colors the effect of the stains, which is of such great importance for the differentiation of tissue. The text portion of the book is admirable, and, while brief, it is entirely satisfactory in that the leading facts are stated, and so stated that the reader feels he has grasped the subject extensively.
William H. Welch, M. D..
Professor of Pathology, Johns Hopkins University, Baltimore.
"I consider Diirck's 'Atlas of Special Pathologic Histology,' edited by Hektoen, a very useful book for students and others. The plates are admirable."
Sobotta and Htiber's Human Histology
Atlas and Epitome of Human Histology. By PRIVATDOCENT DR. J. SOBOTTA, of Wiirzburg. Edited, with additions, by G. CARL HUBER, M. D., Professor of Histology and Embryology in the University of Michigan, Ann Arbor. With 214 colored figures on 80 plates, 68 text-illustrations, and 248 pages of text. Cloth, $4.50 net. In Saunders' Hand-Atlas Series.
INCLUDING MICROSCOPIC ANATOMY
The work combines an abundance of well-chosen and most accurate illustrations, with a concise text, and in such a manner as to make it both atlas and textbook. The great majority of the illustrations were made from sections prepared from human tissues, and always from fresh and in every respect normal specimens. The colored lithographic plates have been produced with the aid of over thirty colors.
Boston Medical and Surgical Journal
" In color and proportion they are characterized by gratifying accuracy and lithographic beauty."
14 SAUNDERS 1 BOOKS ON
Bosanquet on Spirochaetes
Spi rochretes : A Review of Recent Work, with Some Original Observations. By W. CECIL BOSANQUET, M.D., Fellow of the Royal College of Physicians, London. Octavo of 1 52 pages, illustrated. $2.50 net.
ILLUSTRATED
This is a complete and authoritative monograph on the spirochaetes, giving morphology, pathogenesis, classification, staining, etc. Pseudospirochaetes are also considered, and the entire text well illustrated. The high standing of Dr. Bosanquet in this field of study makes this new work particularly valuable.
Levy and Klemperer's Clinical Bacteriology
The Elements of Clinical Bacteriology. By DRS. ERNST LEVY and FELIX KLEMPERER, of the University of Strasburg. Translated and edited by AUGUSTUS A. ESHNER, M. D., Professor of Clinical Medicine, Philadelphia Polyclinic. Octavo volume of 440 pages, fully illustrated. Cloth, $2.50 net.
S. Solis-Cohen, M. D.,
Professor of Clinical Medicine, Jefferson Medical College, Philadelphia. " I consider it an excellent book. I have recommended it in speaking to my students."
Lehmann, Neumann, and Weaver's Bacteriology
Atlas and Epitome of Bacteriology : INCLUDING A TEXT-BOOK OF SPECIAL BACTERIOLOGIC DIAGNOSIS. By PROF. DR. K. B. LEHMANN and DR. R. O. NEUMANN, of Wurzburg. From the Second Revised and Enlarged German Edition. Edited, with additions, by G. H. WEAVER, M. D., Assistant Professor of Pathology and Bacteriology, Rush Medical College, Chicago. In two parts. Part I. 632 colored figures on 69 lithographic plates. Part II. 5 1 1 pages of text, illustrated. Per part: Cloth, $2.50 net. In Saunders 1 Hand-Atlas Series.
PATHOLOGY, BACTERIOLOGY, AND PATHOLOGY. 15
Eyre's Bacteriologic Technique
THE ELEMENTS OF BACTERIOLOGIC TECHNIQUE. A Laboratory Guide for the Medical, Dental, and Technical Student. By J. W. H. EYRE, M. D., F. R. S. Edin., Lecturer on Bacteriology at the Medical and Dental Schools, London. Octavo of 375 pages, with 170 illustrations. Cloth, $2.50 net.
American Text-Book of Physiology second Edition
AMERICAN TEXT-BOOK OF PHYSIOLOGY. In two volumes. Edited by WILLIAM H. HOWELL, PH. D., M.D., Professor of Physiology in the Johns Hopkins University, Baltimore, Md. Two royal octavos of about 600 pages each, illustrated. Per volume: Cloth, $3.00 net; Half Morocco, $4.25 net.
" The work will stand as a work of reference on physiology. To him who desires to know the status of modern physiology, who expects to obtain suggestions as to further physiologic inquiry, we know of none in English which so eminently meets such a demand." The Medical News.
Warren's Pathology and Therapeutics second Edition
SURGICAL PATHOLOGY AND THERAPEUTICS. By JOHN COLLINS WARREN, M. D., LL.D., F. R. C. S. (Hon.), Professor of Surgery, Harvard Medical School. Octavo, 873 pages, 136 relief and lithographic illustrations, 33 in colors. With an Appendix on Scientific Aids to Surgical Diagnosis and a series of articles on Regional Bacteriology. Cloth, $5.00 net; Half Morocco, $6.50 net.
Gorham's Bacteriology
A LABORATORY COURSE IN BACTERIOLOGY. For the Use of Medical, Agricultural, and Industrial Students. By FREDERIC P. GORHAM, A. M., Associate Professor of Biology in Brown University, Providence, R. I., etc. lamo of 192 pages, with 97 illustrations. Cloth, $1.25 net.
" One of the best students' laboratory guides to the study of bacteriology on the market. . . . The technic is thoroughly modern and amply sufficient for all practical purposes." American Journal of the Medical Sciences.
Raymond's Physiology New (3d) ^^^
HUMAN PHYSIOLOGY. By JOSEPH H. RAYMOND, A. M., M. D., Professor of Physiology and Hygiene, Long Island College Hospital, New York. Octavo of 685 pages, with 444 illustrations. Cloth, $3.50 net.
"The book is well gotten up and well printed, and may be regarded as a trustworthy guide for the student and a useful work of reference for the genera! practitioner. The illustrations are numerous and are well executed." The Lancet, London.
16 BACTERIOLOGY, PHYSIOLOGY, AND HISTOLOGY.
Ball's Bacteriology Sixth Edition, Revised
ESSENTIALS OF BACTERIOLOGY : being a concise and systematic introduction to the Study of Micro-organisms. By M. V. BALL, M. D., Late Bacteriologist to St. Agnes' Hospital, Philadelphia. i2mo of 289 pages, with 135 illustrations, some in colors. Cloth, $1.00 net. In Saunders* Question- Compend Series.
" The technic with regard to media, staining, mounting, and the like is culled from the latest authoritative works." The Medical Times, New York.
Budgett's Physiology New od) Edition
ESSENTIALS OF PHYSIOLOGY. Prepared especially for Students of Medicine, and arranged with questions following each chapter. By SIDNEY P. BUDGETT, M. D., formerly Professor of Physiology, Washington University, St. Louis. Revised by HAVAN EMERSON, M. D., Demonstrator of Physiology, Columbia University. i2mo volume of 250 pages, illustrated. Cloth, $ i . oo net. Saundcrs 1 Question- Compend Series.
"He has an excellent conception of his subject. . . It is one of the most satisfactory books of this class" University of Pennsylvania Medical Bulletin.
Leroy's Histology New (4th) Edition
ESSENTIALS OF HISTOLOGY. By Louis LEROY, M. D., Professor of Histology and Pathology, Vanderbilt University, Nashville, Tennessee. i2mo, 263 pages, with 92 original illustrations. Cloth, $1.00 net. In Saunders 1 Question- Compend Series.
" The work in its present form stands as a model of what a student's aid should be ; and we unhesitatingly say that the practitioner as well would find a glance through the book of lasting benefit." The Medical World, Philadelphia.
Barton and Wells' Medical Thesaurus
A THESAURUS OF MEDICAL WORDS AND PHRASES. By WILFRED M. BARTON, M. D., Assistant Professor of Materia Medica and Therapeutics, and WALTER A. WELLS, M.D., Demonstrator of Laryngology, Georgetown University, Washington, D. C. i2ino, 534 pages. Flexible leather, $2.50 net; thumb indexed, $3.00 net.
American Pocket Dictionary New (7th) Edition
DORLAND'S POCKET MEDICAL DICTIONARY. Edited by W. A. NEWMAN DORLAND, M. D., Editor "American Illustrated Medical Dictionary." Containing the pronunciation and definition of the principal words used in medicine and kindred sciences, with 64 extensive tables. 610 pages. Flexible leather, with gold edges, #1.00 net; with patent thumb index, $1.25 net.
" I can recommend it to our students without reserve." T. H. HOLLAND M D of the Jefferson Medical College, Philadelphia.
