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of the membrane, takes place, but that ultimately, however, a very small portion of the cell-cavity remains. What sort of a substance it is that constitutes the elastic parts, has not been determined, because it is not possible to accomplish their solution by any means; with a part of the products of the decomposition of this tissue we are, indeed, acquainted, but nothing further is known concerning its chemical constitution. But from this no decision 'can be arrived at with respect either to its composition, or position in a chemical point of view with regard to other tissues.

This kind of transformation prevails to an extraordinary extent in the skin, especially in the deeper layers of the corium proper, and to it is chiefly owing the extraordinary resistance of this tissue which we so gratefully acknowledge when daily testing it in the soles of our shoes. For the firmness of the individual layers of the skin depends essentially upon the greater or less quantity of elastic fibres contained in them. The most superficial part of the coriuni immediately beneath the rete mucosum is formed by the papillary portion (Papillarkorper), by which we are to understand not only the papillae themselves, but also a continuous layer of coriaceous substance running along horizontally beneath them; it is under this that the coarse elastic networks begin, whilst only fine elastic fibres, and these in a fascicular form, ascend into the papillae themselves, at the base of which they begin to form fine and close-meshed networks (Figs. 16, P, P; 83, A, e; D, c). These latter are connected inferiorly with the very thick and coarse elastic network which pervades the middle and toughest portion of the skin, the corium proper; below this comes a more coarsely meshed network within the less firm, but nevertheless very solid, undermost layer of the cutis, which passes inferiorly into the adipose or subcutaneous tissue.

In the places where such a transformation into elastic tissue has taken place, there are frequently scarcely any

ELASTIC TISSUE OF THE SKIN.

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distinct cells to be found. This is the case not merely in the skin, but also especially in certain parts of the middle coat of arteries, and particularly in the aorta. Here the network of elastic fibres attains such a preponderance, that it is only with great care that minute cellular elements can here and there be detected. In the skin, on the other hand, in addition to the elastic fibres, a somewhat greater number of small corpuscles are found, which have retained their cellular nature, though they are certainly so extremely minute that they must be specially sought for. They generally lie in the interstices of the large-meshed networks, where they either form a system with perfect anastomoses and small meshes, or else appear in the shape of more isolated, roundish bodies, in consequence of the individual cells not being very distinctly connected with one another. This is especially the case in the papillary portion of the skin, which both in its continuous layer and in the papillae contains nucleated cells, in direct contrast with the corium proper, which at the same time is less vascular. But a far greater number of vessels was certainly needed in the former part, inasmuch as they have at the same time to furnish nutritive material for

Fjg. 44.

[graphic]

the whole stratum of cuticle which lies above the papillae; nevertheless, however, there is left only a small quantity of juice at the disposition of the papillae as such. Every

Fig. 44. Vertical section from an injected preparation of the skin. E. Epidermis. R. Rctc niucosum. P. Papillae of the skin, with their ascending and descending vessels (loops). C. Cutis. 11 diameters.

papilla, therefore, corresponds to a certain (vascular) district of the superjacent cuticle, whilst on the other hand it is itself resolved into as many elementary (histological) districts as there are elements (cells) in it.

In the scrotum the subcutaneous tissue (the dartos) presents peculiar interest, from the fact of its being particularly rich in vessels and nerves, quite in accordance with the peculiar import of the part; and besides from its possessing an enormous quantity of muscular tissue, consisting, in fact, of those little cutaneous muscles, which I lately

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Fig. 45. Section from the tunica dartos of the scrotum. Side by side and parallel are seen, an artery (a), a vein (v), and a nerve (n) ; the first two with small branches. On the right and left of them organic muscular fasciculi (m, m), and in the interspaces soft connective tissue (c, c), with large anastomosing cells and fine elastic fibres. 300 diameters.

THE DABTOS. 107

described to you (p. 67). These are the really active elements of the contractile tunica dartos. In this very part, in which formerly a contractile connective substance was considered to exist, the quantity of the little cutaneous muscles is extremely large, and the rugae of the scrotum are produced solely and exclusively by the contraction of these minute fasciculi, which, especially after they have been coloured with carmine, can very easily be distinguished from the connective tissue. They are of pretty nearly the same breadth, broader for the most part than the bundles of connective tissue; and in them the individual elements are arranged in the shape of long, smooth fibrecells. Every muscular fasciculus, after it has been treated with acetic acid, presents at regular intervals those peculiar, long, frequently staff-shaped nuclei, and between them is seen a delicate division of the substance into separate cells, the contents of which have a slightly granular appearance. These are the wrinklers of the scrotum {corruga tores scroti). Besides, we also find in the extremely soft membrane a certain number of fine elastic elements, and in greater quantity the ordinary, soft, wavy connective tissue, with a great number of relatively voluminous, spindle-shaped and reticulated, granular, nucleated, cells.

These persistent cells of connective tissue had previously been totally overlooked, its fibrils having been regarded as its real elements. If, namely, the individual constituents of connective tissue be separated from one another, little bundles are obtained of a wavy form and streaky, fibrillar, appearance. According to Reichert, indeed, this appearance is merely due to the formation of folds, an idea which ought not perhaps to be admitted to the extent in which it was advanced, but which has not been altogether refuted, inasmuch as a complete isolation of the fibrils can never be effected excepting by artificial means. At all events a homogeneous basis-substance, which holds the fasciculi together, must be assumed to exist in addition to the fibrils. This, however, is a question of subordinate importance. On the other hand, it is extremely important to know, that wherever this lax tissue is met with, whether beneath the cutis, in the interspaces of muscle, or in serous membranes, it is pervaded by cells which for the most part anastomose (so as in longitudinal sections to form parallel rows, in transverse ones networks), and separate the bundles of connective tissue from one another, in much the same way that the corpuscles of bone separate its different lamellae. In addition, the most manifold vascular connections are everywhere met with; indeed, the vessels are so numerous, that a special nutrient canalicular system in the tissue might even appear altogether unnecessary. But this tissue also, however favourably its capillary channels may be disposed, stands in need of an arrangement of such a nature as to render a special distribution of the nutritive juices to the separate cellular districts possible. It is only when we conceive the absorption of nutritive matter to be a consequence of the activity (attraction) of the elements of the tissue themselves, that we are able to comprehend how it is that the individual districts are not exposed every moment to an inundation on the part of the blood, but the proffered material is, on the contrary, taken up into the parts only in accordance with the requirements of the moment, and is conveyed to the individual districts in such a quantity, that, in general at least, as long as any possibility of its maintenance exists, one part cannot be essentially defrauded by the others.

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