General Anatomy, Applied to Physiology and Medicine, Vol. 1 (of 3)

by Xavier Bichat

At the end of a period, very different according to the degree of temperature, the arterial texture yields finally to maceration and putrefaction. In the first case, it softens gradually without changing colour, loses the adhesion of its fibres, and is ultimately resolved into a pulp almost homogeneous and greyish. In the second case, it becomes greyish at first, then is reduced also to a pulp, and when all the fluid part is evaporated, there is left a kind of coal wholly different from that which remains after the putrefaction of the muscles. In general, it requires much longer time to soften the arterial texture by maceration than by putrefaction; which shows the superiority of the action of the air over that of water, in the production of this phenomenon.

Exposed to the contact of caloric, the arterial texture curls up, contracts and exhibits the horny hardening in the highest degree. If the action of water is added to that of caloric, which produces boiling, the following is the result of it. 1st. Very little froth rises before ebullition, from the vessel that contains the arterial texture; we might say that this texture and the muscular present in this respect, two opposite phenomena in the economy; the small quantity of froth that arises from the first, is greyish. 2d. At the moment of ebullition, there is an evident horny hardening, less however than that of the nervous texture, more sensible in the direction of the diameters than in that of the axis; a hardening accompanying this horny hardening, and a yellowish tinge of the liquor. 3d. This state continues for half an hour or more, ebullition constantly going on. 4th. Successive softening; but at the same time a greyish tinge succeeding to the yellow colour; want of adhesion among the fibres, increasing as the ebullition goes on, so that they break with great ease. 5th. However prolonged may be the ebullition, the arterial texture is never reduced, like the fibrous, the cartilaginous, &c. to a gelatinous and yellowish pulp. The fibres remain as they are, in the same relation, with the same size, &c. The want of adhesion and the change of colour are almost the only phenomena they experience. 5th. The broth, produced by the boiling, is insipid and tasteless, a proof how few neutral salts the arterial texture contains.

The action of the concentrated acids curls this texture, afterwards softens it, finally dissolves it in the form of a pulp, yellowish by the nitric, and blackish by the sulphuric.

Most of the others have a less sensible action than these two. When they are diluted, there is no horny hardening at the moment the artery is immersed in them; but its texture is gradually softened, and can be broken with the least effort, as after boiling. It is never reduced to a fluid state, how long soever it may continue in the acid.

The alkalies, even the caustic, have but little action upon the arterial texture; immersed a long time in them, this texture remains almost untouched, loses but little by solution, cannot be broken as it can after being in the diluted acids, &c.

Membrane common to the system with Red Blood.

I call that the common membrane which lines the arteries, the left side of the heart and the pulmonary veins. It can be dissected with ease upon these two last organs. To separate it from the arteries, it is necessary to cut through by a very superficial circular section, the external fibrous layer, raise this layer by laminæ from below upwards; we come then to the internal membrane, which adheres but little to the preceding, and can be detached from it in the form of a canal, of very great extent. It is distinct from it, 1st. by its extreme tenuity, and the transparency that results from it; 2d. by its white colour; for it appears yellow only by being applied to the preceding; 3d. by the entire want of fibres. It is smooth and with a uniform texture like the serous membranes, which we may be convinced of by holding it up to the light. Besides, it differs essentially from these membranes by a kind of brittleness that characterizes it; it is broken and torn by the least effort. The whole resistance of the arteries resides in their fibrous coat.

It appears that this membrane, though every where connected, has however some differences of structure in the different regions. 1st. It is evidently more delicate in the interior of the ventricle with red blood, than in the corresponding auricle and in the arteries. 2d. It yields in the heart and in the pulmonary veins, to dilatations much greater than those of which it is susceptible in the arteries, in which it would inevitably break, like the proper membrane, if the blood could produce as great differences of size in it, as it does in these organs. 3d. When we macerate the heart for some time, this internal membrane acquires in the auricle and upon the mitral valves, a very remarkable whiteness, and which is foreign to it in all the rest of its course. 4th. As to the action of the different agents, of the air, of water, of caloric, &c. it appears to me to be the same every where, and resembles precisely that upon the peculiar membrane. Only I have thought, that in the small arteries, the common membrane has the horny hardness more than this, which on this account wrinkles on the interior in different places, when a whole branch is immersed in boiling water; this does not take place in the great trunks.

It is evident from this, that though the common membrane of red blood, is every where continuous, it is not uniform in its structure; we shall have occasion to make an analogous observation for the different portions of the two general mucous surfaces.

The internal surface of this membrane is moistened in the dead body, by an unctuous fluid, that is found in greater or less quantity. Does this fluid exist in the living? does it serve to defend the arterial coat from the impression of the blood? It is difficult to determine. We know of no organ fitted to furnish it; it would arise from the exhalants, if its existence, as many authors have admitted, was real. It would be well to ascertain as to its existence, whether it was merely a transudation after death, analogous to that of the bile through the gall bladder, or the consequence of a little serum remaining in the arteries after the expulsion of the blood. What makes me suspect so is, that these arteries being deprived of blood, contract intimate adhesions on their internal surface; which their fluid ought to prevent, as that of the mucous tubes does, which should they cease to transmit their respective substances, as the excrements for example, the secreted fluids, &c. would never be obliterated because of this fluid.