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

by Xavier Bichat

We call by this name those small eminences that arise from the external surface of the chorion, and which, piercing the capillary net-work of which we have just spoken, become by their extremities contiguous to the epidermis. These eminences are very evident in the palm of the hand and the sole of the foot, where they are regularly arranged, in the form of small curved striæ in different directions. We see them through the epidermis, notwithstanding its thickness in these places. But they are seen especially when this has been in any way removed, as by maceration, ebullition, &c. If we cut longitudinally a portion of the chorion of the foot, with its epidermis adhering to it, we see between them along the divided edge, a line in the form of a curved thread, which arises from these small eminences placed at the side of each other.

In some other parts of the skin, we distinguish the papillæ in a very evident manner; but in a great number, the epidermis being removed, we see only a surface, slightly uneven from some small eminences, especially towards the orifices through which the hairs and the vessels pass, but we do not discover those regularly arranged eminences, the papillæ properly so called.

We must not mistake for them the numerous and very evident prominences, which render the skin of some subjects extremely rough. These prominences are formed by small cellular, vascular or nervous bunches, by sebaceous glands, &c. which are found near the small openings by which the chorion opens under the epidermis, and usually transmits the hairs. These bunches, lodged in the small oblique canals which are terminated by these openings, raise the external side of them and thus form this prominence. The following very curious experiment proves this arrangement; when the skin is macerated for two or three months, or even less, on the one hand these little bunches in which there is almost always a little fat, are changed into that white, thick, unctuous matter, analogous to spermaceti, into which fat kept a long time in water is always converted; and on the other, the foramina enlarging, as we have seen, and the skin changing into a kind of pulp, we can easily remove it all around these little prominences, and see that they are continued with the fat which fills the meshes of the subjacent chorion, and which is also changed into a hard matter.

Injections have evidently proved to me that there were vessels in these cellular bunches, and I have been convinced of it for some time past by the dissection of some subjects that died of scurvy, in whom the spots commenced by very small ecchymoses, similar as it were to flea-bites, and which occupied these little eminences. The petechiæ of adynamic fevers have a different appearance; but they belong also to an extravasation of blood in the cellular texture, occupying the small pores which open on the exterior of the chorion to transmit the vessels, the hairs, &c. The more prominent these eminences are, of which we have spoken, the more uneven is the skin. In general they are more frequent on the extremities and on the back, than on the anterior part of the trunk. In the extremities there are more of them in the direction of extension, than in that of flexion.

We attach the idea of a beautiful skin, to that in which these small tubercles are not found, and in which the chorion is united at its external surface. Women have commonly this last arrangement more evident than men. The epidermis which covers these eminences very often scales off at that place, especially from strong friction, which contributes still more to render the skin uneven, rough and harsh to the touch where they exist, which might induce a belief that they are formed by it, though it is always only accessory to them. Where it is very thick, as in the palm of the hand and the sole of the foot, it cannot be raised, and these small cutaneous tubercles are never seen. In the face where many vessels pass from within outwards, by the little pores of which we have spoken, we meet with hardly any more of them. The papillæ scattered among these eminences, are in general very slightly apparent in the places where they exist.

All anatomists attribute to these last a nervous structure; they regard them as the termination of all the nerves that go to the skin, and which, according to them, are expanded to form these, after having first left their external covering. Some even say that they have traced filaments even into the papillæ; I confess that I have never been able to do it. In the ordinary state, the density of the chorion and the extreme delicacy of the filaments, are evidently an obstacle to it. In the state of long continued maceration, in which the chorion becomes pulpy and in which we might consequently trace these filaments, were it ever possible, it cannot be done. I do not however deny the texture attributed to the papillæ. The acute sensibility of the skin seems even to suppose it; but it is only analogy and not demonstration, which establishes this anatomical fact; indeed all the other senses, whose organs are so sensible, have the portion of them which receives the impression of bodies continuous with a nerve.

Action of different bodies upon the Dermoid Texture.

In most of the other textures, we have only considered this action in the dead body, because during life, these textures always removed from external bodies, cannot be influenced by them. Here we can regard it in a double relation, since the skin is incessantly in contact with almost all the bodies of nature.

Action of Light.

Light evidently acts upon the dermis. Removed from its influence, men are blanched, if we may so say, like plants. Compare the inhabitant of a city, who is never exposed to the influence of the sun, with the peasant who constantly is, and you will see the difference. It appears that it is the light and not the heat which produces the effect of which I have already spoken; for individuals who live in a warm temperature, but removed from the solar light, become white like those of cold countries. Thus we know that some men who keep their chambers always very hot, are whiter than others who, living in a less hot atmosphere, are constantly exposed to the sun. We might remain forever in a bath of a temperature equal to the warmest seasons, and the skin would not blacken. Apartments for study which are warmed with stoves, and in which men remain as long as the labourer at his plough, are as warm as the atmosphere of summer, and yet the skin of those who occupy them never becomes darker. Besides an irresistible proof is that the clothing which does not prevent the action of caloric upon the skin, and which offers a barrier to the rays of light only, prevents the cutaneous colouring that takes place upon the parts which the light immediately strikes, as upon the hands, the face, &c.