Imagens das páginas
PDF
ePub

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

[merged small][graphic]

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.

[blocks in formation]

described to you (p. 57). 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 rugæ 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 (corrugatores 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 lamellæ. 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.

LECTURE VI.

MARCH 3, 1858.

NUTRITION AND CIRCULATION.

Arteries. Capillaries. - Continuity of their membrane.—Their porosity.— Hæmorrhage by transudation (per diapedesin).-Veins.-Vessels during pregnancy.

Properties of the walls of vessels:

1. Contractility.-Rhythmical movement.-Active or irritative hyperæmia. -Ischaemia.-Counter irritants.

2. Elasticity and its importance as regards the rapidity and uniformity of the current of blood.-Dilatation of the vessels.

3. Permeability.-Diffusion.-Specific affinities.-Relation between the supply of blood and nutrition.-Glandular secretion (liver).-Specific action of the elements of the tissues.

Dyscrasia. Its transitory character and local origin.-Dyscrasia of drunkards. -Hæmorrhagic diathesis.-Syphilis.

I HAVE endeavoured, gentlemen, in the last two lectures to present to you a somewhat detailed picture of the more delicate arrangements which prevail in the body for the conveyance of the different currents of nutritive juices, and particularly for the conveyance of those currents in which the juices themselves are more hidden from observation. Allow me to-day to pass on to the consideration of the larger channels and nobler juices, which, according to prevailing opinion, stand more in the foreground.

The distribution of the blood takes place, as is well known, within the vessels in the following manner : The

arteries divide into finer and finer branches, and whilst they thus divide, the character of their walls gradually undergoes such alterations, that at last minute canals, the so-called capillary vessels, appear, provided with a membrane as simple as any that is ever met with in the body. The histological appearances which present themselves in these different vessels are as follows:

On isolating an artery we find that its walls are relatively very thick, and in those arteries which can be followed with the naked eye, not only the well-known three coats are distinguished with the help of the microscope, but in addition to these a fine epithelial layer, which invests the internal surface and is not wont to be included in the class of structures usually termed coats. The internal and external coats are essentially formations of connective tissue, which in the larger arteries display a continually increasing quantity of elastic fibres; between them lies the relatively thick middle, or circular-fibre, coat, which, as being the seat of the muscular fibres, constitutes what may be almost termed the most important component of the arterial walls. These muscular fibres are found in the greatest abundance in the middle-sized and smaller arteries, whilst in the very large ones, and especially in the aorta, elastic layers form the predominant constituent even of the circular-fibre coat. In small arteries on microscopical examination there may be easily observed within this coat (Comp. Figs. 26, b, b; 45, a) little transverse striations, corresponding to the individual fibre-cells, and encircling the vessel in such dense array, that we find fibre-cell by the side of fibre-cell without any interruption. The thickness of this layer can be readily estimated in consequence of the well-marked limits set to it upon the in- and out-side by the longitudinal-fibre coats ; the only deceptive appearance is presented by certain round bodies, which are to be seen here and there in the substance of the circular-fibre coat, but only at the border of the

« AnteriorContinuar »