Book - A textbook of histology, including microscopic technic (1910) Special Histology 2

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Böhm AA. and M. Von Davidoff. (translated Huber GC.) A textbook of histology, including microscopic technic. (1910) Second Edn. W. B. Saunders Company, Philadelphia and London.

A Textbook of Histology (1910): Introduction To Microscopic Technic | General Histology | I. The Cell | II. Tissues | Special Histology | I. Blood And Blood-Forming Organs, Heart, Blood-Vessels, And Lymph- Vessels | II. Circulatory System | III. Digestive Organs | IV. Organs Of Respiration | V. Genito-Urinary Organs | VI. The Skin and its Appendages | VII. The Central Nervous System | VIII. Eye | IX. Organ of Hearing | X. Organ of Smell | Illustrations - Online Histology
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Special Histology

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 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

1. 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 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 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 networks 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 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 structure. It is divided by means of elastic fibers and membranes (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 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.

Fig. 171. Cross-section of the human carotid artery ; X J 5'

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

Fig. 173. Precapillary vessels from mesentery of cat : a, Precapillary artery ; b, precapillary vein possessing no muscular tissue.

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 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 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.

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

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 preparations, 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 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.

Fig. 176. Endothelial cells of capillary (a) and precapillary (b) from the mesentery of rabbit ; stained in silver nitrate.

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 parenchyma 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 kidney, 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 areas of the skin (ear, tip of nose, toes) and in the meninges, kidney, etc.

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

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

1. 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.

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.

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 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 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.

Fig. 178. Section of a cell-ball from the glomus caroticum of man ; X I ^- (Injected specimen, after Schaper.)

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 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 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 1 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 1 vol. 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 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 apoplectic 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 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 the ampulla). The pipette is then carefully shaken to mix thoroughly the blood and the diluting fluid.

Fig. 179. Thoma-Zeiss hemocytometer: a, Slide used in counting ; b, sectional view ; f, a portion of ruled bottom of the well ; </, pipette.

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.

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 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.


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.

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.

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A Textbook of Histology (1910): Introduction To Microscopic Technic | General Histology | I. The Cell | II. Tissues | Special Histology | I. Blood And Blood-Forming Organs, Heart, Blood-Vessels, And Lymph- Vessels | II. Circulatory System | III. Digestive Organs | IV. Organs Of Respiration | V. Genito-Urinary Organs | VI. The Skin and its Appendages | VII. The Central Nervous System | VIII. Eye | IX. Organ of Hearing | X. Organ of Smell | Illustrations - Online Histology

Reference: Böhm AA. and M. Von Davidoff. (translated Huber GC.) A textbook of histology, including microscopic technic. (1910) Second Edn. W. B. Saunders Company, Philadelphia and London.

Cite this page: Hill, M.A. (2020, January 29) Embryology Book - A textbook of histology, including microscopic technic (1910) Special Histology 2. Retrieved from,_including_microscopic_technic_(1910)_Special_Histology_2

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