Part 25

The cutaneous exhalants do not appear to be everywhere equally abundant. The face and chest contain many of them; we sweat easily in these places. On the back and the extremities they are less numerous. It is rare that we sweat on the palms of the hands and the soles of the feet. Besides this varies remarkably in different individuals. I know two sisters, belonging to a family in which phthisis has been frequent, whose chests are however well formed, and who have never had any sign of an affection of the lungs, and yet when they are warm they always sweat from the chest. We know that in some the sweat appears most usually in the face, and in others on the cranium.

Have the nerves any influence upon the cutaneous exhalation? In many cases of paralysis, the patients sweat from the sound side. I have attended, for two months past, a man at the Hôtel Dieu, who after an apoplexy, had hemiplegia so that the left side of the body was immoveable, and who only sweats from this side, so that an evident line of demarcation is visible the whole length of the median line. On one side the skin is dry, and on the other it is very moist. I know cases are related in which opposite phenomena have taken place; but they do not destroy the observation that is uniformly made, that the sweat takes place equally upon the sound and the diseased side. Besides, who does not know that when the nervous action is annihilated in a limb, a blister acts upon it as usual? Do convulsions, in which the nervous action is so much raised, increase cutaneous exhalation? Have the states of extreme sensibility, in which all the cutaneous nerves are so susceptible of receiving all impressions, the least known influence upon sweating? Let us acknowledge then that in cutaneous exhalation, as in secretion, we know nothing of the nature of the nervous influence, if it does exist.

_Sebaceous Glands._

Besides the insensible transpiration and the sweat, which are thrown out by the skin, this organ is constantly lubricated by an oily fluid, which occasions, when coming out of a bath, the water with which it does not unite, to collect in small drops upon the body, which greases the linen when it remains too long in contact with the skin, catches the dust that is floating in the air, makes, it remain upon the skin, and retains many foreign substances coming with the sweat from without or within.

This fluid is in general much more abundant in negroes, whose skin is on this account disagreeable, than in European nations in whom it abounds especially in places provided with hair, particularly on the cranium. If left without dressing, the hair becomes greasy, unctuous and shiny; it seems even that this abundance of oily fluid is destined to support their suppleness. Thus art imitates nature in the preparation of it, and greasy substances almost always enter into the dressings of the toilet. It appears that there is less of this fluid in other parts where there are hairs. It oozes in very small quantity from the soles of the feet and the palms of the hands, no doubt on account of the thickness of the epidermis. When we wash these last, the water collects in small drops on the back of them, and not in the palms, which are easily and uniformly wet; there is never any of it deposited on the surface of the nails. This cutaneous oil, retained in certain places, as in the axilla, the perineum, the folds of the scrotum, &c. becomes mixed there with certain principles of the transpiration, and often exhales a fetor that is almost insupportable.

This oily fluid, of the nature of which we know but little, is not like the transpiration or the fat exposed to evident increase and diminution; it is always found in nearly the same proportion. It appears to preserve the suppleness of the skin, by preventing it from cracking. The ancients sought no doubt to imitate its action over the whole skin, as we imitate by pomatum its functions in regard to the hair, by the oily unctions which they made upon the body. This we know was much practised among the Romans.

Whence comes this cutaneous oil? It can be furnished from three sources, 1st, from transudation; 2d, secretion; 3d, exhalation.

Some have thought that the sub-cutaneous fat oozed through the pores to form it; but the scrotum which is destitute of this fat is one of the most oily parts. The skin of the cranium, which is so to the highest degree, is hardly at all fatty. That of the cheeks which covers much fat, is scarcely lubricated with it, &c. In emaciation the skin is often as unctuous as in corpulency, though it is not always the case. Finally, in all the other functions, physical transudation is proved to be nothing; would it exist then here alone?

Those who admit the secretion of the cutaneous oil, (and they are the greatest number,) place the source of it in the small glands that are called sebaceous, and which they say are every where spread under the skin. We see some small tubercles upon the convexity of the ear, upon the nose, &c.; but in most of the other parts it is impossible to distinguish any thing; we see only the small eminences of which I have spoken and which make the skin rough; now they have nothing in common with these glands, the existence of which I do not deny, but which I confess I have many times in vain sought for.

This has made me think that there is perhaps an order of exhalants destined to separate the cutaneous oil, and which is distinct from that of the exhalants which throw out the transpiratory matter. There is in the cellular texture exhalants for fat and others for serum. Certainly no gland presides there over the secretion of the fat. It is the same with the marrow which the exhalants of the medullary membrane furnish. There is I think as much probability in the supposition of the exhalation, as of that of the secretion of the cutaneous oil.

Besides, we must not confound this oil, either with that ceruminous matter which certain glands pour out on the edges of the eyelids and behind the ears, and which is forced out by pressure in the form of little worms, or with that whitish substance that is collected between the glans and the prepuce, and which is so evidently furnished by small glands.

ARTICLE THIRD.

PROPERTIES OF THE DERMOID SYSTEM.

I. _Properties of Texture._

These properties are much developed in the skin. The alternations of emaciation and corpulency through which our organs, the limbs especially, pass sometimes from a determinate size to one double or even treble, and afterwards return to their primitive state, prove these properties; and so do all the different tumours, deposits of pus, external aneurisms, sudden engorgements which accompany great contusions, aqueous collections in the abdomen, pregnancy, scirrhi, numerous affections which increase the size of the testicle, hydrocele, &c. We see in all these cases the skin at first extended and dilated, then contracting when the cause of the distension has ceased, and occupying the place in which it was originally circumscribed.

The remarkable separation which the two edges of a wound experience, that is made by a cutting instrument, is owing to the contractility of texture. This separation which takes place upon the dead body, proves what we have already often remarked, viz. that the properties of texture, absolutely inherent in the organic texture, are foreign to the vital forces from which they only borrow an increase of energy; thus the cutaneous retraction is much stronger during life in a longitudinal or transverse wound. But it is particularly in amputation that we observe this increase of contractility from the vital action. No part, not even the muscles retract so much as the skin; hence the precept so much recommended in this operation of saving the integuments as much as possible; hence the essential modifications that have been made in the ancient methods. The muscular retraction is more sudden; but this, which is more durable, ultimately prevails; so that in the ancient mode of amputation, where every part was cut at the same level, they had a conical stump, the summit of which was formed by the bone, in which was next seen the muscles, arteries, &c. and in which the skin representing the base, terminated on the side of the limb.

There are however many cases in which the dermoid extensibility is less than it at first seems to be. For example, in large sarcoceles, the skin of the neighbouring parts of the scrotum being drawn, is applied upon the tumour, and makes up for the extensibility that is wanting in the skin of this part; that of the penis especially is almost wholly employed to cover the tumour; so that this organ disappears. It is to the limits placed to the cutaneous extensibility that must also be referred the following phenomenon; in a wound with loss of substance, the fleshy granulations, in contracting by the evacuation of the white substance that filled them, draw the neighbouring skin in order to cover the wound; now this drawing produces not only an extension but a real locomotion. Hence why when the skin, naturally tense and adherent, cannot yield to this locomotion, the cicatrices are formed with so much difficulty, as we see upon the cranium, the sternum, &c.; why on the contrary on the scrotum, the fold of the axilla, &c. they take place with so little; why in dissecting out tumours, it is so much recommended to save the sound integuments, &c.

When the skin is stretched, the fibres which compose the spaces that have been spoken of, separate from each other, and these spaces become broader. Their breadth becomes especially evident on the internal surface of the dermis; for as all the pores of the external surface pierce obliquely its texture, the distension of this texture only diminishes the length of the small canal they form, but does not enlarge the orifice of it; thus whilst the internal surface contains interstices of considerable size, this remains uniform, but allows us to see these interstices, which render it more transparent where they exist; hence that appearance like marble on the skin of the abdomen of women who have had many children.

When the skin is contracted, the internal spaces are drawn together and even effaced. The external surface which has none of these, cannot diminish so much in breadth, so that there is a disproportion in the breadth of the internal and external surface; hence, as I have said, the convexity of the latter in the horny hardening produced by boiling water; hence also the inequalities and external roughness which takes place when cold acts powerfully upon us, and which contracts the dermoid texture. Besides, this phenomenon only takes place when the contractility is evident in the ordinary state; for if there has been previous distention, the cells already enlarged, return only in contracting to their natural state, and there is no disproportion in the extent of the internal and external surfaces of the skin.

In most of the extensions, there is a diminution of the thickness of the dermoid texture. It is only when it is dilated by the infiltration of water in its spaces, as in leucophlegmasia, that it increases in thickness by diminishing in density. In chronic inflammation, in engorgement, and in various alterations of which the dermoid texture is the seat, it loses in part the faculty of stretching; it breaks with ease when it is distended. This is what happens in some aneurisms, in those of the aorta especially that have produced an absorption of the sternum. A slow inflammation seizes upon the skin that covers the tumour, and it breaks with a degree of distention infinitely below what it bears in a sound state, if the death of the patient does not prevent this fatal rupture, two examples of which I have seen in the ward of lying in women at the Hôtel Dieu. In this state of inflammation, the distention is very painful, whilst it is not so in the ordinary state.

The skin loses also its contractile power in most of the chronic affections of which it is the seat, and which alter its texture.

Are there some days in which the skin is more contracted, and others in which it is looser and more expanded? I believe so, from observing the marks left after small-pox, which are much more apparent and deeper some days than others.

II. _Vital Properties._

These are strongly marked in this system. We might say, that nature by giving an excess of life to this dermoid covering, has wished to establish a striking line of demarcation, and to make us perceive the difference between the inorganic bodies with which its external surface is in contact, and the organized textures that its internal surface covers. I shall consider these vital properties as in all the other systems; some belong to animal life and others to organic.

_Properties of Animal Life._

The animal sensibility exists in the highest degree in the skin. It presides over the feeling, which is more acute and delicate there than in most of the other textures. It is also the cause of touch, a double function which is very different.

The feeling is the faculty of perceiving the impression of the surrounding bodies. It gives us the sensations of heat and cold, moisture and dryness, hardness and softness, &c. It has relation then, 1st, to the existence; 2d, to the general modifications of external bodies. Its exercise precedes that of all the other senses which cannot be exercised until after its action. It is necessary to the sight, to hearing, smelling and the taste, as it is to the touch. It depends only upon a particular modification of the animal sensibility; it is nothing but this property considered in exercise. Thus when the particular modifications of this sensibility which preside over the other senses have been destroyed, when the eye is insensible to light, the ear to sounds, the tongue to tastes and the pituitary membrane to odours, these different organs still preserve the faculty of feeling, both the presence of bodies and their general attributes.

The touch has only relation to the particular modifications of bodies; it is the source of our notions upon their external forms, their dimensions, size, direction, &c. It differs essentially from the four other senses.

1st. In this, that it does not require, like the feeling, any particular modification of sensibility. The hand is a little more sensible than the rest of the skin; but there is not a great difference, and we should touch bodies almost as well, if that of the abdomen covered the phalanges. On the contrary, each sense has a peculiar sensibility which places it exclusively in relation with a determinate body in nature. The pituitary membrane would be struck by light in vain, if placed at the bottom of the eye like the retina; the palatine membrane if it lined the nasal fossæ, would not perceive odours, &c.

2d. The touch is exercised only upon masses, more or less considerable parcels. The other senses are brought into action by the insensible and infinitely multiplied particles of bodies, as the luminous, savoury particles, &c.

3d. Most of the other senses do not require the previous exercise of the will. Odours, light and sounds strike upon their respective organs, and often produce, without our attending to them, their respective sensations. It is the same with feeling; the will most commonly has no part in it. It is exercised because we live in the midst of many excitements. We do not most often seek for the causes of general sensations; they are those that come and act upon us. On the contrary, the touch requires to be produced by an act of the will. It is exerted in consequence of the exercise of the other senses; it is because we have seen, heard or felt an object, that we touch it. We confirm or correct by this sense the notions, which the others have given us. Hence why it is, as it were, dependant on them. The more they are contracted, the less frequently is it exercised. The blind, the deaf, &c. have less desire to touch than him, who has all his sensitive gates open to the impression of external bodies.

4th. Most of the other senses require a peculiar structure as well as a peculiar sensibility in the organs which compose them. On the contrary, the touch only requires a particular form in its organs. Provided that these have on the one hand animal sensibility, and on the other can embrace by many points external objects, they can distinguish their tangible qualities. The touch will be obscure if we grasp bodies in one or two directions only; yet it will take place. Thus we touch with the hollow of the axilla, the bend of the arms, hams, &c. with the lips and with the tongue. Thus the elephant touches with his trunk, reptiles by twining themselves around bodies, most animals with their snouts, &c. But the more the points of contact are multiplied, the more perfectly is the sense exercised. The hand of man is in this respect the most advantageously formed; it proves that he is better adapted to communicate with what surrounds him than all other animals; that the empire of his animal life is naturally much more extended than that of theirs; that his sensations are more accurate, because they have a means of perfection that theirs have not; and that his intellectual faculties are destined to have an infinitely greater sphere, since they have an organ infinitely better than theirs to perfect them.

The sensibility of the skin resides essentially, as we have seen, in the papillary body; it is there that all the great phenomena relative to sensation take place. It is this portion of the skin that truly belongs to animal life, as the reticular body is, on account of the vascular plexus that forms it, the portion essentially dependant on organic life. The chorion being as it were passive, remains foreign to every kind of important function, and serves only for a covering.

The extremely acute sensibility of the papillary body requires a covering to defend it from strong impressions. This covering is the epidermis. When it is removed, every touch is painful; the impression of the air even is very much so; it is this removal of the epidermis that produces the smarting that is felt when a blister is taken off. Observe in fact that smarting is a very frequent kind of pain, which the animal sensibility of the skin occasions when more raised than usual. This term[1] is borrowed from burns, which, when they are only to a certain extent, acting nearly like blisters, lay the papillæ bare; now as it is always the skin which is exposed to the action of fire, we transfer to all burnt organs the ideas which we attach to the word smarting. But the pain is far from having the same character in the other systems; this peculiar one belongs only to the dermoid, in which it takes place from a burn, erysipelas, after a blister, &c. and during all inflammations that have their seat in the reticular body. No other system when inflamed gives us this sensation. The pain is throbbing in the cellular; it exhibits a wholly different modification in the muscular, when it is the seat of acute rheumatism, &c.

[1] In order to understand this sentence it should be observed that the word which I have translated smarting is _cuisson_, which means the action of fire upon animal bodies, and is also used for the painful sensation which this action produces.—TR.

There is another kind of pain which is also peculiar to the cutaneous system; it is itching, which is the first degree of smarting. We remove it by a gentle friction, which exciting in the papillæ a different sensation, effaces that of which they are then the seat; but when this new sensation has passed off, the former one, which is occasioned by a permanent cause, is reproduced and requires a new friction; there happens then in a small way, what we observe in a large one, when a stronger pain makes us forget one that is weaker. No other system in the economy exhibits this kind of pain, so frequent in itch, herpes and many other cutaneous eruptions. In their tubercular inflammations, the serous membranes become the seat of white eruptions, analogous to many of those of the skin; the mucous surfaces are also often affected with many small pimples; now this sensation is never manifested in either of them.

There is also a sensation which appears to be the minimum of that pain of which smarting is the maximum; it is tickling, a mixed sensation, an hermaphrodite, as an author has called it, which is agreeable when carried to a certain degree and painful beyond it. Carry the fingers lightly over a mucous or serous surface, a muscle or a nerve laid bare; an analogous sensation will never arise from the contact.

The animal sensibility of the skin is, like that of the mucous surfaces, subjected to the essential influence of habit, which can transform successively into indifference or even into pleasure, what was at first painful. Every thing that surrounds us furnishes constant proof of this assertion. The air in the succession of the seasons, caloric in the numerous varieties of the atmosphere, in the sudden change from one temperature to another, water in a bath, in the moist vapours with which the medium is loaded in which we live, our garments of which some, as those of wool, are at first very painful, every thing which acts upon the skin by mere contact, produces sensations in it which habit continually modifies. Observe the mode of dress of different nations; in some, all the superior extremities are bare; in others, the fore-arm only appears; the inferior extremities, either in whole or part, are naked in others; in some, a more or less considerable portion of the trunk is left exposed to the air, and among the savages, nothing is covered. The portions which in each people remain naked, bear the contact of the air, without giving any painful sensation. Let them expose, on the contrary, parts usually covered, especially if it is cold, and at first pain will be the consequence of it; then the parts gradually becoming accustomed to this contact, will get to be insensible to it. There has been much said latterly of the danger of the Grecian costumes, of the nudity of females, &c. I do not speak of the morality of them; but every thing that is reprehensible physiologically is, that the progress of the fashion has been more rapid than that of the sensibility. If they had exposed at first the neck, then a little of the chest, then the bosom, &c. habit would by degrees have given a new modification to this property, and no accident would have resulted from it. But in going suddenly from a costume in which every part is covered, to that in which the superior half of the chest, either before or behind, remains naked, is it astonishing that colds, catarrhs, &c. should be the result of it?