Meckel1812-1 Anatomy 2-1

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Meckel JF. Handbook of Pathological Anatomy (Handbuch der pathologischen Anatomie) Vol. 1. (1812) Leipzig.

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General Anatomy. Part II

Section I. Of The Mucous System

§ 47. The mucous system,{l) or cellular tissue, {tela seti textusmucosus, cellulosus, crihrosus,) is one of the two elementary forms to which, in ultimate analysis, the whole organic formation may be referred. It is the coagulable fluid coagulated. It is generally described(2) as an assemblage of numerous layers, and of soft and white fibrils, which, varying constantly in their aiTangement, produce cellules of different sizes and forms. All these cellules communicate, so that the whole tissue forms but a single cavity which is infinitely subdivided, from which circumstance its most common name, cellular, is derived. But when closely examined, it is perceived that this assertion is at least too general, and that the mucous tissue is a cohesive, homogeneous, viscous, shapeless, and but slightly solid substance. It appears thus in the inferior animals, and in the commencement of all formations. In fact, we see at first only this homogeneous semi-fluid mass, in which globules afterwards appear, and concur to form the whole organism. There exists primitively between it and these globules, and afterwards between it and the organs, the same relation as between the shapeless portion of the fluids, and the globules which swim in them.

(1) D. C. Schobing-er, De telÅ“ cellulosÅ“ in fabricâ corporis humani dignitate, Goetting-en, 1748. — Thierry, E. incelluloso textujrequentiiismorbict morborummutationes, Paris, 1749, 1757, 1788. — Hunter, Remarks on the cellular membrane and some of its diseases, in the London Med. Obser. and Inquiries, vol. ii. p. 26. — Th. Bordeu, Recherches sur le tissu muqueux ou cellulaire, Paris, 1767. — J. Abadie, Diss. de corpore cribroso Hippocratis, seu de textu mucoso Bordevii, Montpelier, 1774. — C. P.VVolff, De telâ, quam dicunt cellulosâ,obsermtiones: in the Nov. Comment. Petropol., vol. vi. vii. and viii. — Detten, Bcylrag zu der Lehre von der Verrichtung des Zellgewebes. Munster, 1800. — Lucæ, Anatomisch-physiologische Bemerkungen über den Zellstoff: in the Annalen der Wetterauer Gesellschaft für die Naturkunde, vo\. ii., 1810. — G. R. Treviranus, lieber die organischen Elemente des thicrischen Koerpers ; in Vermischte Schriften, vol. i. 1816, p. 124. — Pelici, Cenni di una nuova idea sulla natura del tessuto cellulare, Pavia, 1817. — Heusinger, System der Histologie, Eisenach, 1823, Part II. p. 121.

(2) This is the view taken by Haller, Bergen, Sohobinger, and Thierry. This opi nion was adopted by Bichat, and recently by Béclard and Blainville, and is now generally received in Ensland, Prance, and Italy. Bordeu's opinion, which Meckel follows, has been defended in Germany by Wolff, Autenrelh, Prochaska, Blumenbach, Rudolphi, Treviran us, and Heusinger. F. T.

We may be convinced of the exactness of tlfis representation at all periods of fife. Neither layers, fibres, nor cells, are perceptible to the naked eye, even when aided by a microscope, and we see only the substance spoken of by us, without the least opening. This substance appears to be composed of fibres and layers only because its viscidity causes it to assume that form when it is extended, and with or without a microscope these layers and fibres may be seen to form under the eyes of the observer. When, for instance, we separate two muscles or muscular fascicuH, the homogeneous substance between them becomes at first uneven, and appears filled with chamrels, without always losing its cohesion. But if this traction be continued, or if more force be used, it tears and produces filaments or small cyhndrical columns, which become very long if the extension be sustained. If we cease to extend it, so that the space occupied by the substance is diminished, the filaments fii'st shorten and finally unite anew in a coherent mass.

When the mucous tissue is extended, air sometimes accidentally penetrates it and produces vesicles of different sizes and figures. But this air escapes when the tension ceases and the tissue then assumes its primitive form. The cellules which arise in this manner are not always the same, for if these parts be again separated the ah' penetrates anew, but the cells nowformed are very different from the fii'stboth in size and form. When these cells remain by continued extensions, the air is confined only by the contraction of the mucous tissue at the moment when the traction ceases, so that, when renewed, cells of the same form are naturally produced. When air penetrates into the mucous tissue, it can be pushed in every dhection ; we can divide or reunite the vesicles to which it gives rise, and thus vary their form to infinity.

The facts which Bichat(l) regarded as proving that the mucous tissue is an assemblage of filaments and laminæ, demonstrate only that, when properly considered, this substance can assume this form, whenever the circumstances are favorable. Thus, for instance, it is pretended that the distension of a part of the mucous tissue of the scrotum would demonstrate its lamellar and fibrous structure, because it then appears as a transparent membranous layer, presenting many irregular filaments, which are seen when more force is used, as the spaces between them are then enlarged. But this experiment only proves that whenever the homogeneous mucous tissue is distended, it can assume the lamellar and the fibrous form.

Accordingly, then, as we simply extend the part, or at the same time inflate it with air, and as the substance is more or less viscid, we obtain in the same part either vesicles of different sizes, or filaments, or, finally, both vesicles and filaments, at the same time we then see simple meshes, or true permanent cells.

Nor does the cellular structure obtained by congelation prove that this arrangement is original. As the mucous tissue is always filled with bquids, the interstices they occupy must become permanent by freezing.

These pretended fibres have also been called absorbent or exhalent vessels, because they are discovered only in those portions of the mucous tissue which have been formed into membranes by extension, and have not been observed in those parts which have a cellular form from the introduction of the air. But it is easily perceived that this difference also depends on the process employed ; for traction ought necessarily to produce fibres ; while distension by air, which acts in every direction at once, gives rise only to laminae and vesicles.

The color of this semi-transparent substance is grayish. The white tint commonly attributed to it does not belong to it, but results only from the reflection of light from an infinite number of surfaces when laminæ and filaments have been artificially formed. The term mucous tissue already adopted by Bordeu, is then more exact than that of cellular tissue which is generally used.

§ 48. All the phenomena presented by the mucous tissue are explained with as much, and even with more facility, by the hypothesis of this structure, than of that of the formation usually attributed to it.

The most remarkable property of this tissue is its penetrability or permeability. Foreign substances which are accidentally introduced, or which are abnormal only from their great abundance, are frequently seen in parts the most distant from where they entered ; or when they form a coherent mass, they sometimes extend through the whole tissue and sometimes are expelled only by one opening.

Here we may mention,

1st, The migrations of those firm solid bodies which have penetrated into the organism. Thus, pins which have been introduced into the stomach proceed to the fingers, the toes, or the other regions of the surface of the body, as the loins, sides, &c. Often too they are carried from the surface into other parts, and move from the arm towards the chest — from the hand towards the upper part of the arm, &c.

2d. The facility with which general emphysema is produced by blowing air into any portion of the body, and the ease with which the air passes out from a single opening.(l) Air, if introduced under the skin penetrates, not only below the cutaneous organ and the parts covered by it in the whole body, but also within the interstices of the muscles and into the substance of aU the viscera. The same thing happens after wounds of the lungs ; the air which is constantly renewed by respiration, passes, first, through all the branches of the bronchial system in its mucous tissue, and from thence into every part, so that the body often resembles a large bladder distended by air.

3d. The ease with which collections of pus point at a distance. The pus of abscesses developed in the chest bm-rows a passage to the feet through the mucous tissue which fills the interstices of the organs, Urine, which filters through a wound in the bladder, penetrates the cellular tissue of the abdomen, and even of the chest. The blood from a wounded artery spreads itself through the cellular tissue of an entire limb, &c.

4th. In a general anasarca all the serum sometimes escapes by an accidental or artificial opening, if the nature of the fluid will permit.

These phenomena are commonly attributed to the continuous communication of the celhdes with each other ; but they may be explained as well by the softness and semi-fluidity of a cohesive substance. All these unusual passages are but temporary, and it is evident that many of the above mentioned phenomena, as the migrations of foreign bodies, and of collections of pus, favor the hypothesis of the cellular structure of the tissue less than that of its mucous structure, for it is not probable that these bodies would follow the direction of the cellules. They burrow, remoiung, destroying, and separating, purely mechanically, the mucous tissue before them : in the former case the tissue is reproduced, or collapses when they have passed ; in the latter case the disease, which at first was slightly developed, is now extended. If we be incorrect, how do bodies which have been swallowed descend from one cavity to another ? How do pins proceed from the intestinal canal into the vessels 1 Why is the mucous tissue altered at all points where it contains pus ? None of these phenomena demonstrate a cellular structure, and many prove the contrary.

§49. The relations of the. mucous tissue with the organs are of two kinds ; it forms, or does not form, one of their essential parts. In the first place it may be called the internal or special mucous tissue, in the second, the external, or general mucous tissue.

The former contributes to form the organs, either alone or combined with nerves, vessels, or a pecuhar substance which pervades it ; the second is found between the organs, and fills the mtervals between them. But at the same time both unite ; for the external mucous tissue gradually blends with that which properly belongs to the organs.

(1) We have seen several of these general emphysemas which so commonly follow wounds of the lungs, and which sometimes result from the rupture of a cartilaginous ring of the trachea. Air penetrates into the mucous tissue very rapidly, but when a large opening is made forÂî, but little escapes, even when we press around the wound. Most probably, then, it is absorbed, rather than expelled. F. T.

As the mucous tissue of the organs penetrates all their substance, the distinction between the internal and external mucous tissue is not very strict, and the whole body is imbedded in mucous tissue. The most essential difference between these two tissues relates only to the functions. The internal mucous tissue contains the different substances which form the organs, while the external includes only the fat and serum, which are necessary for their continual reproduction, and also for their constant activity.

§ 50. The external mucous tissue may, nevertheless, be considered as forming, in some measure, a separate system: for in the different regions of the body it is connected with the internal mucous tissue less intimately than with its own peculiar parts. Setting aside both this internal tissue and the organs it assists to form, it represents an uninterrupted system, which is a duphcate of the form of the whole body, but which, in certain parts, differs considerably in regard to quantity, cohesion, and the nature of the fluids it contains. Besides the general connections between all the portions of the mucous tissue there are places where those of the principal regions, which correspond with the principal regions of the body, pass more particularly and imperceptibly from one to the other. Although these details may belong strictly to special anatomy, they should be anticipated here, since we must know them to acquire a complete idea of the mucous system.

The mucous tissue exists but in a small quantity within the vertebral column and the skull ; the cavity of the spine contains more than the skull, especially between the dura mater and its bones : and there also it contains an abundance of fat, which is not found in the cranium. This phenomenon is very remarkable, since in several animals, particularly in most fishes, a very coirsiderable mass of fat is found within the cranium between its paiietes and the brain which is small in relation to the capacity of the cavity, so that the substance scattered between the organs, as nutrition in reserve, exists at least where the brain is still very imperfectly developed.

On the contrary, much mucous tissue exists around the vertebral column, and there is always more before than behind, and also around the head.

In the trunk this tissue abounds, not only around the vessels which proceed along the vertebral column the aorta and the vena cava,*in the thoracic and abdominal cavities, in the neck around the carotid arteries, the jugular veins, the pneumogastric and sympathetic nerves, and the esophagus, but it accumulates in great quantities in several parts of those regions. On the sides of the neck, at its upper part, it surrounds the numerous lymphatic glands and the salivary glands, and below, the vessels and nerves of the upper extremities as they emerge from thethorax. It abounds in the chest in the twomediastina and around the large vessels : and without this cavity, especially at its superior part, it exists around the mammary glands, and also between the two pectoral, and the senatus magnus, muscles. There is more in the abdomen than in the chest, particularly around the kidneys and at the entrance of the vessels into the abdominal viscera, between the folds of the peritoneum, and especially in the mesentery. But in no part is it more abundant than in the pelvis, around the rectum, the internal organs of generation and the bladder, and it thus favors the great enlargement of the parts within this cavity. It accumulates also on the outside of the pelvis and principally forward in the external genital organs, the scrotum, and the labia pudenda. On the external surface of the skull there is less than in the face where large masses exist in the orbits of the eyes, between the muscles of the face, in the cheeks, and around the mouth.

In the limbs its quantity is in a direct ratio with the extent of motion in the different regions. It is most abundant in the axilla and in the groin ; and there is more in the former than in the latter ; less is found in the succeeding articulations. There is not so much between the muscles of the arm and of the thigh, as between those of the fore arm and the leg, and of the hand and the foot.

The masses of internal and external mucous tissue communicate together in the different regions of the body, principally by the openings of these regions and the spaces between them. These are then the points through which abnormal substances pass from one region to another.

The mucous tissue of the cavity of the spine, communicates with that which covers the spinal column externally, principally by the intervertebral foramina; and the mucous _ tissue of the cawty of the skull is connected with that of the exterior of the skull and of the face by openings for the passage of the nerves, as also by the great and small emissary veins. That of the face is continuous, particularly on the sides of the lower jaw, with the mucous tissue of the neck ; this mucous tissue of the neck unites with that of the thoracic cavity, in the place where the vessels and nerves of the arm emerge from the thorax ; this proceeds to the abdomen along the large vessels, especially the aorta, and along the esophagus also, passing through the openings in the diaphragm designed for the passage of these canals, and gliding at the same time through the smaller perforations in this muscle. The mucous tissue of the abdomen communicates with that of the organs of the pelvis by the inguinal ring, the crural arch, the sciatic notch, the foramen ovale, and the lower cavity of the pelvis.

§ 51. The mucous tissue immediately connected with the organs, for which we caimot find a better term than special, also divides into two parts : the external serves to envelope each organ, continues itself imperceptibly with the general mucous tissue, and forms the transition from the general to the special mucous tissue : the internal, on the contrary, concurs with the materials coming from the other systems to form the organs.

The external portion of the special mucous tissue forms around each organ a layer which separates it from the rest. We may say, then, with Bordeu, that this tissue represents a kind of atmosphere. This separation, as a layer, is produced, first, by the peculiar life of the mucous tissue ; secondly, by the fat and serum with which it is filled,

The most important organs, then, are generally imbedded in the largest masses of this tissue, whenever they are not insulated by other modes ; although, in certain cases, this result is produced by the two arrangements united.

In the organs formed of several superimposed layers, as the alimentary canal, the bladder, &c., a proper layer of mucous tissue always exists between the different coats, which may be regarded as forming the transition of this to the internal mucous tissue ; since, if it is internal in regard to the whole organ, it is also external in relation to each of its different layers.

Partly on account of these atmospheres of mucous tissue, the adjacent organs and the superimposed layers of an organ, escape for a time the diseases which attack one or more of them. Nevertheless, the mucoos tissue does not insulate them perfectly, so that, in general, the disease of an organ or layer finally passes through it, and attacks the organ or layer adjacent ; and again it only serves to concur in the insulation of the diseases of the organs which depends principally on the peculiar structure of each part, and on the differences of the life it enjoys. This proposition seems at least very probable, when we remember that, although the nerves and vessels are not lined with this tissue, they often escape disease, although all around may have been destroyed by suppuration ; the character of the disease itself has also some influence, for some maladies extend to the surrounding parts more readily than others.

Further, these atmospheres of mucous tissue relate also to the motions of the organs, and hence are found abundantly around parts which are very movable.

§ 52. Usually it encompasses the respective parts in their whole extent, except the skin, where it is found only on its internal face. Hence the skin has been compared, in this respect, to the serous and mucous membranes, and even to the vessels ; but the comparison is incorrect, since all the hollow organs are enveloped in all parts with the mucous tissue. In fact their internal surfaces are not lined with it, so that, when opened and drawn out to reduce them into flat membranes, they are analogous to the skin. And will not all the other organs present the same phenomenon if they are also treated in this manner ? Finally, the skin is no exception to this rule, as the epidermis, which covers it, may be considered as an indurated mucous tissue, and as an external envelope or capsule.

§ 53. The proper substance, the vessels, and the nerves, of the organs, are situated within the special mucous tissue, which may itself be divided into two other parts. Each branch of a vessel, of an excretory duct, or of a nerve in the interior of an organ, has its layer, its proper cellular sheath, which is more solid than the rest. Between these sheaths we find a looser mucous tissue. The fascicuh and the fibres of a muscle are surrounded with proper sheaths, which are arranged, in regard to the looser mucous tissue in their spaces, in the same manner as is the capsular mucous tissue of a whole organ in regard to the general mucous tissue. The final element, which possesses a definite form, is also enveloped with mucous tissue.

Thus, in final analysis, the mucous tissue represents a cavity constantly folding from without inward, which closely envelopes the whole body, and all the organs, and even their minutest portions.

We cannot perceive with the naked eye in all the organs, that the quantity of the mucous tissue is in an equal ratio with the other compound elements included by them ; many seem even entirely destitute of it. Thus we find hitle in the brain, spinal maiTOw, bones, tendons, &c., while there is much more in the muscles and the lobate glands.

§ 54. Although some vessels and nerves of large and small caliber, wind into the mucous tissue, we cannot consider them as its component parts, since they pass through it only to go to the organs and form with it their bases. But the most dehcate ramifications of the exhalent and absorbent vessels,(l) undoubtedly enter into its organization, and very probably have no proper parietes distinct from the rest of this tissue.

As regards chemical composition, the mucous tissue belongs to the class of organs formed principally of gelatine.

§ 55. -The mucous tissue is highly elastic, so that it may be extended to a great degree, and contracts in the same proportion ; its elasticity, however, is diminished by the effects of inflammation and other morbid changes, and it becomes fragile.

The plastic or formative power, is developed in it to a great degree ; hence its facility of prompt and complete reproduction, when it has once been destroyed ; and hence too it replaces those parts which cannot be reproduced in perfection, as the muscles and the tendons. All reproduction then commences by the formation of mucous tissue. This tissue is destroyed with difficulty. The other vital phenomena, irritability and sensibility, are not observed in it ; at least it possesses the former only in certain regions, and in a feeble degree ; and even the phenomena which lead to this conclusion do not positively prove it, since they may occur in the muscular system or in the cutaneous tissue, as well as in the mucous system.

§ 56. The mucous tissue mcludes two different fluids, a serum., analogous to that of the blood, and fat.

(1) Absorbent and exhalent vessels do not exist. They have never been seen, but have been imagined, to account for the phenomena of exhalation and absorption. Before they were thought of, these phenomena were well explained by transudation and imbibition. Physiologists owe this doctrine to Magendie and Fodera. Fodera thinks that exhalation and absorption depend on capillarity of the tissues, that this double phenomenon can exist in all parts, and that the liquids which they contain may be carried either by the lymphatics or by the arteries and veins. See his Recherches experimentales sur V absorption et l'exhalation, Paris, 1824. F. T.

The serum, unlike the fat, exists in all parts, but not always in the same quantity, which seems to be inversely as that of the fat ; thus it abounds in the scrotum and eyelids, which normally contain no fat, and it collects there more readily than in other places ; an accumulation of it constitutes anasarca. The serum of the mucous tissue, like all the serous fluids, contains an abundance of albumen combined with a small quantity of coagulable mucilage and salts. If we may judge from experiments made upon the serum which is collected abundantly by blisters between the cutis and epidermis, the ratio of the animal matter to water, is less than in the serum of the blood.(l)

§ 57. The fat(2) is yellowish and less fluid than the serum of the mucous tissue. This substance occurs in masses of various forms, composed themselves of regular, rounded globules or vesicles arranged more or less compactly, one against another. The masses and vesicles are formed of mucous tissue, which contains the fat, but is not connected with it, and which unites them altogether. Their size varies, although Wolff pretends it is always the same in man, for the small masses which they inclose, differ much in volume. The largest are generally situated internally, and continue diminishing as they approach the circumference, where they are also more compact. Nevertheless small masses are found among the large. These have the same volume in all the regions of the body, although that of the masses varies infinitely.

In regard to chemical composition, fat differs from all other animal substances, as it contains but very little azote : by distillation it is resolved, for the most part, into water and carbonic acid, and a small quantity of ammonia. A peculiar acid, which Krell believed he had discovered in fat, seems not to exist ; as is the case too with the salts and acetic acid mentioned by Thenard,(3) while the peculiar acid he thought he discovered in fat, is benzoic acid, (4) according to Berzehus.(5)

The quantity and nature of the fat is not the same every where.

This substance presents itself in two states loose, and in combination.

There are parts of the body which contain no loose fat, as the interior of the skull, of the brain, of the eye, of the nose, of the organ of hearing, the lungs, the intestinal canal, and the glands.

Much is found, however, under the skin, except in the penis, eyelids, and scrotum. It abounds in the face, the neck, the abdomen, the groins,

(1) Marcet, A chemical account of carious dropsical fluids, int\ie Medico-Chirurg. Transac., vol. ii. p. 34-384. Bostock, On the analysis of animal fluids, in same journal, vol. iv. p. 63.

(2) Malpighi, De omento, pinguedine et adiposis ductibus ; in his Epist. anat., London, 1686, p. 33. — Jansen, Pinguedinis animalis consideratio phys. et pathoL, Leyden, 1784. — Wolff, De adipe, in Nov. Act. Petrop., vol. vii. 1789, p. 278. — Reussing, Diss. de pinguedine sand et morhosä, Jena, 1791. — Allmcr, Diss. sistens disq. anat. pinguedinis animalis, Jena, 1823.

(3) Ueber die Fettsaure, in Scherer's Allgem. Journ. de Chemie, vol. viii. p. 127.

(4) Heber die Fettsaure, in Gehlen's Journ. für Chemie und Physik, vol. ii. p. 275.

(5) Chevreul has recognized in it, as in many other fatty bodies, two portions, a fluid called elain, and a solid called stearin ; this latter very much resembles the fat of tallow, but is distinguished from it, as by saponification, we have margaritic but not stearic acid. It is white and has but little lustre ; when fused it crystalizes on cooling in small needles, the mass of which is terminated by a plane surface. As to elain, it is colorless, and resembles an oil ; it is liquid even at four degrees below zero, and begins to form an acicular mass at several degrees below this temperature. It is inodorous, or nearly so : its taste is sweetish, and when fresh is not disagreablc. F. T.

the upper parts of the extremities, the palms of the hands, the soles of the feet, between the voluntary muscles and among their fasciculi and even their fibres, around certain membranes, as the peritoneum and its prolongations especially the omentum and mesentery, in the pelvis, beneath the internal layer of the pericardium, consequently on the surface of the heart, around the origins of the large vascular trunks, in the mediastina, around certain glands, as the salivary glands and kidneys, around the nerves penetrating between their fasciculi in considerable quantity, and finally within the bones, especially the long bones, where it is called marroti;. (1)

It accumulates in those parts especially which execute extensive and frequent motions, and in those where it is necessary that the heat should be concentrated. It is deficient, on the contrary, in fat persons, where it would incommode the functions, and where its existence might atfect even life.

The fat, combined with the other immediate materials of organized bodies, exists in several places where it is rarely found in a loose state, and where even it is never uncombined, as particularly in the brain, (2) which, like the nervous system in general, contains a considerable quantity of the two different fatty substances.

The fat does not exist in the substance of the fibrous organs, in the cartilages, bones, or serous membranes, either in a loose state or in combination ; although it sometimes collects in considerable quantities around those parts.

The fat has not the same consistence every where : thus, it is very hard around the kidneys, but softer on the heart and in the orbits of the eyes.

G. Hunter was led to conclude, from the constant deficiency of the fat in some parts of the body while it abounds in others, from a greater accumulation of serum or air in parts destitute of fat in persons affected with edema or emphysema, while, whatever degree of obesity occurs, fat never accumulates in these parts even when they are so situated that a fluid contained in the mucous tissue would collect in them from the fact of its gravity alone, as the scrotum ; fi'om the difference observed too, even in the most extensive anasarca, between those parts of the mucous tissue filled with water and those which before contained fat ; and from another circumstance, that the fatty portions of the mucous tissue do not yield at all to pressure, as do those which contain an excess of serum, and that the fat usually cannot pass from one place to another ; all these facts, we say, led G. Hunter to conjecture that the fat is secreted by a peculiar glandular apparatus, distinct from the common mucous tissue, and composed of vesicles. (3)

(1) Analysis of the marrow by Berzelius, in Gehlen's Journal für Chemie und Physik, vol. ii. p. 287.

(2) Vauquelin, Analyse de la matière cérébrale de l'homme et de quelques animaux, in the Ann. du Muséum naturel, vol. xviii. p. 212-239.

(3) Wolff was the first to state that the molecules of fat are contained in the spaces of the mucous tissue in which they are placed, and not in special cells. Heusinger

Most probably, howerer, this special apparatus does not exist, and the adipose cellules are all produced simply bj' fatty globules, which penetrate the mucous tissue as the fat forms. Our opinion is founded too on the circumstance of the fat appearing in the form of globules independently of the mucous tissue, of which we may be easily convinced by destroying a lump of it.

Riegels opinion is stiU less probable : this physiologist thinks that fat is formed in aU the glands, but principally in the renal capsules.(l)

Fat has several uses. Its tmctuous nature facilitates the motions of the organs ; it is a bad conductor of caloric, and hence it protects them from cold by opposmg the dispersion of the animal heat. Finally, it serves particularly as a reserve of nutriment, although, as it contains no azote, it is but feebly animalized. Farther, as its formation is favored by rest, so those organs which remain for a long time unused, even the muscles among the rest, are transformed into fat ; on the contrary, lasting, intellectual and bodily labor, and debihty from any reason, cause it to disappear. The facüiiy of its production doubtless depends on its shght degrees of animalization ; hence the reason why it appears, not only in the circumstances above mentioned, but also to replace those parts which are wasted, and which have been removed ; as, for example, the testicle in the scrotmn or the eye in the orbit when they have been extirpated.

§ 5S. The mucous tissue and the fluids it contains differ very much in several respects at different periods of life. Like all other parts, they are more fluid in proponion as the organism is younger. The mucous tissue appears at first absolutely homogeneous, very soft, and differs but shghtly or not at aU from serosity, from which it is afterwards distinguished by its greater sohdity. Hence the reason that during the early periods of hie we can easily separate parts which afterwards become inseparable ; this is seen panicularly in those parts which are formed of several superimposed ‘ layers united by mucous tissue.

The mucous tissue is more abundant the younger the drganism is. The organism originally, when homogeneous, is formed of this tissue alone ; even after the organs are developed, its proportion is stfll much greater, as it contains few substances which are pecuhar to it. This is proved by the muscles, whose fascicuh are small in proportion to the mucous tissue, and by the glands, which are composed of several lobes, united by a loose mucous tissue, and easily separable from each other.

The fat is more hquid, t hinn er, more transparent, and whiter, the nearer the organism is to the time of its origin. Xor is its quantity the same at all periods of hfe. In the early periods of fetal existence

adopted this opinion ; bnt Beclard has rejected it, and, faithfal to the old doctrinesj »dmits a special adipose tissue, even as he adopts the opinions of Bichat's school, in regard to the structure of the mucous tissue. F. T.

(1) De tisu s'ljr.dularum suprarena/ium in animalibus, necnon de origine adîpis, disquieiiio ariaiomico-phps-iologica, Copenhagen, 1790. Riegel has explained the uses of the fat very clearly, although his little work contains cnany arbitrary assertions wholly unproved, partly true or entirely false.

it is deficient in those organs which afterwards contain the most. It begins to appear at the fifth month under the skin in small isolated masses. It exists in masses in this place only, even in the fuUy grown fetus ; for the internal parts,, even those where it afterwards abounds, as the epiploon, the heart, the surface of the kidneys, the muscles, &c., have none or but very little, while it is formed in abundance near the surface of the body. This arrangement resembles that in the cetaceous animals, where httle is found mtemaUy, but enormous masses exist near the external surface of the body. It gradually increases also internally ; but, generally speaking, tliis occurs only towards the middle of hfe. At puberty the fat diminishes externally, as it does in the hibernating animals, in proportion as the semen is secreted with more acti\ity,(l) and m the same manner also, as in insects, the genital organs develop themselves at its expense, so that the neuters and those which lose their sex are fatter than the others.

Finally, the fat not unusually disappears in all parts of the body at an advanced age, and the subject actually wastes. The extremities of life then are alike in this respect. Nevertheless, the body of the old man differs fi'om that of the infant, in that, although the layers of fat diminish in him, the organs are still proidded with it, and consequently the body always possesses it in a large quantity. A severe and long continued dropsical affection can alone remove it entirely, which depends doubtless on the fact that the abundant formation of the serum prevents that of the fat.

§ 59. The mucous tissue forms the basis not only of the regular but also of the irregular tissues. The history then of all the alterations of texture might be given in this place, since they develop themselves near it and in it ; but as these alterations present peculiar characters, as they appear in the mucous tissue of some organs rather than in that of others, we had better mention them when speaking of those organs of which they are repetitions, or in which they are developed.

The induration- oi the mucous tissue is rather a common morbid alteration, and occurs most frequently hi very young children. It attacks particidarly that found under the skin. The fat and serum seem to participate in it also, for ff we cut into the indurated mucous tissue, a yellowish fluid escapes.

^ The serum of the mucous tissue accumulates morbidly in general anasarca. In this disease the fat disappears more or less completely, and is converted hito a mucous substance analogous to gelatm.

The fat itself often varies from the normal state, piincipaUy as respects its quantity. We have already pointed out in a summary manner the circumstances of its excess or deficiency. Its general or local accumulation is sometimes enormous. Generally speaking, it increases in those parts where it is found in a state of health rather than in any other, although in other places the ordinary proportion exists : we have observed this particularly in the great epiploon. The same may be said of the surface of the heart and mediastinum. Thus, it is in the epiploon that lipomata are most frequently formed. But we must not confound these congestions of fat with the lardaceous tumors, Avhich do not deserve this name, as they are simple condensations of the cellular tissue, or re^'-^titions of other regular tissues, or finally peculiar morbid tissues.

(1) H. Reeve, De animalibus hyeme sopitis, London, 1803. — Idem, An essay on the torpidity of animals, London, 1809. — Mangili, Saggio di osservazioni per serrire alla storiade' i mammiferi soggetti al perioclico letargo, Milan, 1807- — Idem, Mémoire sur la léthargie périodique de quelques mammifères, in the Annales du Muséum, vol. x. p. 234. — J. A. Saissy, Recherches expérimentales, anatomiques, chimiques, etc., sur la physique des animaux mammifères hibernons, Paris, 1808. — Prunelle, Recherches sur les phénomènes et les causes du sommeil hivernal de queU ques mammifères, in the Annales du Muséum, vol, xviii. p. 20.

The lipomata almost always perfectly resemble the normal fat ; we rarely find them surrounded with a proper cyst ; they are connected intimately with the adjacent fat, although from their size and prominence they are immediately discovered. Those below the skin may be confounded with other diseases, especially with hernias, when they are developed in those parts where the viscera appear after leaving their cavities ; of this we have seen several instances, and have some preparations m our cabinet.

Fat, however, develops itself sometimes irregularly where it does not exist in a natural state : as first in the ovaries, then on the internal face of the mucous membrane of the intestinal canal, and rarely within the skull. In the ovaries we often find hair developed with the fat ; and as in the normal state the mucous tissue contains both fat and serum, so collections of the latter fluid are almost always found in those ovaries which are overloaded with fat.

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Reference

Meckel JF. Handbook of Pathological Anatomy (Handbuch der pathologischen Anatomie) Vol. 1. (1812) Leipzig.

Volume 1. Table of Contents

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Cite this page: Hill, M.A. (2024, April 20) Embryology Meckel1812-1 Anatomy 2-1. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Meckel1812-1_Anatomy_2-1

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