DERMOID SYSTEM. (continued 2)

I wished to know what is the state of the respiratory fluid in summer, in which there is much transpiration, and in which all the heterogeneous principles consequently go out by the skin. To obtain this fluid which is exhaled in insensible vapour, I placed a clean, empty bottle in a pail filled with ice and the muriate of soda, and I respired a long time in it, taking care not to allow any saliva to fall in. The parietes, chilled by the external ice, condensed into small icicles the vapour of my breath, on the internal surface of the vessel. When I had made a certain quantity of these, I withdrew the bottle; then by putting it into tepid water, the icicles immediately melted, and I had in a liquid state my respiration, which was before in vapour. Now I have been struck with two things in this experiment, 1st, with the small quantity of fluid that I was able to obtain, though I had respired for an hour, and afterwards made two men respire each an hour; 2d, with this, that most of the reagents have no action upon this fluid. Nitric, sulphuric and muriatic acids, lapis infernalis, and alkohol produce no effect when mixed with it. In evaporating a small quantity in the concavity of a watch chrystal, no residuum is left; placed in a spoon over the flame of a candle, it experiences no alteration from the heat. In a word, I have been almost tempted to believe that it was nothing but water. I confess however that this experiment ought to be carefully repeated.

The little fluid obtained made me believe that the form of the vessel was not well adapted to the purpose, because it did not present sufficient surface and the vapour of the lungs was too little divided. I took then the spiral cylinder of a small alembic which I surrounded with ice in a pail; I made a man breathe through it, and I obtained in fact more fluid, but infinitely less however than I expected, considering the great cloud that is formed in winter by respiration. In an hour, two ounces of fluid only were condensed, which I weighed comparatively with water, and found a little heavier, a proof that some principles are mixed with its aqueous portion, and with which I am unacquainted.

I am convinced that in winter I should have condensed much more vapour; the inspection of an animal that breathes proves it even, as I have just said. I am persuaded also, that like the urine, the respiratory fluid is then charged with principles which, during summer, pass off by the skin, though I have not however any experimental data upon this essential point, which I propose to clear up the approaching winter. I think even that many colds depend upon this. In fact, many of these principles thrown out by the mucous surface of the bronchia, not soluble in the air, like their aqueous vehicle, stagnate upon this surface, irritate and excite a cough which throws them off. On this account, we cough much in winter, as we have often occasion to bathe in summer, when the saline substances, which are accumulated upon the skin by the exhalation that takes place there, cannot be evaporated by the air. Hence why also in many affections of the lungs, in which the mucous glands and the bronchial exhalants do not increase the quantity of fluid they usually pour out, but only separate with it, on account of their change of organic sensibility, substances which the air cannot dissolve, hence, I say, why in these affections there is a constant cough; for, as I have said, when a substance remains for any time upon the mucous system, it irritates, and it makes an effort to get rid of it. I believe that this elucidates the cause of many coughs, which have been considered as nervous, on account of the small quantity of expectoration, and which are only a means that nature employs to supply the want of the evaporation of the air.

I think that physiologists have not paid sufficient attention, either as it respects the bronchia or the skin, to the part which can be evaporated, and to that which cannot. Some animals seem to throw out more of these principles that cannot be evaporated, than man; hence why it is necessary to curry horses every day, and even to bathe them often, in order to cleanse their skins which the air would leave dirty. Fourcroy and Vauquelin have remarked that there is never phosphate of lime in the urine of these animals; this substance appears to pass out with the sweat, and to be chrystalized on the surface of the skin, from which it is removed by friction and water. I can hardly conceive how the hairs can be the emunctories of it; it appears to me to be more natural to think from analogy, that it is by the sweat that it escapes. I presume that the rain, in the natural state is as necessary to these animals as to plants. The first do not avoid it; many even expose themselves to it; it serves as a bath for them, removes the saline particles the air does not dissolve, and washes the skin.

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 term1 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.

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?

Habit extends its empire, in relation to the skin, even to our manners themselves. Decency is in this respect a thing of comparison. An Indian woman, with nothing but a narrow cloth around the pelvis, would be with us an object at which the public modesty would be shocked. The habit of mankind serves her as a veil in her own country. A female savage transported entirely naked to the same country, would be indecent there; she is not so in her own. Observe our fashions in their rapid succession; a woman, who by not changing her costume, would have had two years since, that of a courtezan, would now find herself dressed with great modesty. Indecency in costume is that merely which shocks our habit. The female Indian, with the rag that covers only a quarter of her body, is more decent than the woman in whom a small opening separated the neck-handkerchief in our old fashions. The sight of the face shocks those people among whom females are veiled. Let us consider then habit as the type of the decency of costumes. Nature has wished in physiology, that the phenomena over which it presides, should be slowly connected; it is the same in morals. The woman who suddenly changes her dress from one that is close to one that is not, exposes herself to painful sensations, to catarrhal diseases, &c. and shocks the eyes of those who had been accustomed to see her in a different exterior. When the change is gradually and insensibly brought about, neither health nor morals are affected.

Habit does not modify the cutaneous sensibility which arises from an alteration of texture, from an inflammation, &c. Powerfully raised in this last state, it is much above its natural level. Then the least contact becomes extremely painful; thus the skin is no longer then in a state to exercise the sense of feeling. The touch itself does not distinguish general sensations. All bodies make a common and uniform impression, it is that of pain.

The animal sensibility of the skin sometimes diminishes and even disappears; paralysis is a proof of this. These affections, more rare than the loss of motion, often however take place. In the organs of the senses, it is the eye which most frequently loses the sensation; the ear comes next, then the skin, then the nostrils and finally the tongue, which is the sensitive organ that is always most rarely paralyzed, no doubt because it is that which is the most connected with the support of organic life, without which we could not exist. The others belong especially to animal life, which we can lose in part without ceasing to exist.

The whole skin is never at the same time paralyzed; there is rarely even hemiplegia in this respect; the feeling is not extinguished but in an insulated part. I would remark that the existence of these paralyses is also a proof of the want of nervous influence upon cutaneous exhalation and the capillary circulation, since both go on very well in this case as well as in paralysis of motion, as I have observed above. Cut the nerves of a limb of an animal, in order to render this limb insensible; if after this you apply an irritant, the skin will inflame as usual.

When the animal sensibility is in exercise, is there a kind of erection of the papillæ that they may feel more acutely? The same observation may here be made as was in regard to the mucous surfaces. This erection is an ingenious idea of some physicians, and not a fact which rests upon observation. I even think that this contradicts it; for examined with a glass the papillæ appear to be constantly in the same state. Why should not the skin feel like a nerve laid bare, like the eye, the ear, &c. in which these sorts of erections have never been imagined?

Animal contractility is wholly foreign to the cutaneous organ, which moves voluntarily only by the influence of its fleshy pannicle.

Properties of Organic Life.

Organic sensibility and insensible contractility exist in the highest degree in the cutaneous organ. The external capillary system, which forms the reticular body, is, as I have said, especially the seat of these properties. They are in constant activity in order to preside, 1st, over the capillary circulation; 2d, over exhalation; 3d, over absorption; 4th, over the nutrition of the whole dermoid texture; 5th, over the secretion of the cutaneous oil, if the sebaceous glands exist. It is not astonishing that these properties should be so much developed in the skin, in which they have so many functions to support. Add to these considerations the constant action of external bodies, an action which keeps this organ in continual excitement, which incessantly stimulates its sensibility, which is to this sensibility what that of the bodies contained in the mucous surfaces is to the sensibility of these surfaces; the irritation is even more sensible, because the stimuli are oftener changed. A thousand agents of nature, of different density and composition continually succeed each other on the exterior of the body, and at the same time that they act upon the animal sensibility of the skin, to produce various sensations, they excite the organic sensibility in order to support the functions over which this sensibility presides.

Is it astonishing then that the greater number of cutaneous diseases supposes an alteration in this property and in the insensible organic contractility which is not separated from it? I divide these diseases into four classes, according to the structure we have distinguished in the skin.

1st. There are diseases of the papillæ; these are the paralyses and various kinds of increase of feeling, which reside only in the nerves. Women are especially subject to these last, which are so great in some nervous affections, that mere contact of the skin if considerably powerful produces convulsions. To this also should be referred the extreme susceptibility of some individuals in whom tickling produces a general revolution. It is necessary to distinguish these exaltations of animal sensibility, from those of which we have spoken above, and which depend upon inflammation. The organic sensibility is especially affected in these last; we might say that by its increase it is transformed into animal sensibility; whereas in the other case this last property alone is altered.

2d. There are diseases which have evidently their seat in the cellular texture which occupies the dermoid spaces; such are the inflammations of the cutaneous portion which covers a phlegmon, a bile, &c.

3d. There are diseases of the external capillary net-work, from which the exhalants arise. To this must be referred erysipelas, many species of herpes, measles, scarlatina and many acute cutaneous eruptions that are daily met with in practice.

4th. Finally, there are diseases in which the chorion is affected. Elephantiasis, and in general many chronic cutaneous diseases appear to me to be of this number, and I will even observe that the chorion never appears to be primarily affected in acute diseases. The obscurity of its vital forces, its dense and compact texture, and its comparative want of vessels prevent it from accommodating itself except to chronic affections. In phlegmonous erysi pelas, in biles, &c. it is only influenced, but it is not essentially diseased. Thus we have seen that all the affections of the osseous, cartilaginous, fibrous, fibro-cartilaginous systems, &c. are really slow and chronic, on account of the texture and the vital obscurity of these systems.

Now if we reflect on this division of cutaneous diseases, we shall see that except those of the first class, which are not numerous and which consist in greater or less alterations of animal sensibility, we shall see, I say, that all the others suppose a more or less considerable affection of the organic sensibility and of the corresponding insensible contractility. All are derived from an increase, a diminution or an alteration of these properties.

It is also to the different changes of these properties, that must be referred the more or less copious sweats and the various exudations of which the skin is the seat. In fact, the exhalant vessels remain always the same in relation to their structure. Why then do they admit a greater or less quantity of fluids? Why at certain times do they allow of the passage of substances, which they repel at others? It is because the modifications of their organic forces are changed. These forces are often weakened in an evident manner in diseases; they become languid and are prostrated. Then blisters are applied in vain; the organic sensibility no longer answers to the excitement that is made upon it. This is a striking phenomenon in ataxic fevers, and proves the independence of the phenomena of cutaneous exhalation, capillary circulation, &c. in regard to the cerebral nerves. In fact, whilst during the paroxysm the brain is in extreme excitement, the voluntary muscles are put by this excitement into a violent state of convulsion, and the energy of the whole of the animal life seems to be doubled before it ceases to exist, the organic is already in part exhausted; the functions of the portion of the skin which belongs to this life have already ceased.

The stimuli of cutaneous organic sensibility vary remarkably in their degree of intensity. 1st. The strongest are fire, cantharides, the alkalies, the acids sufficiently diluted by water not to act but upon the vital forces and not to alter the dermoid texture by the horny hardening, the juices of many acrid and corrosive plants, certain fluids even produced in the economy, as those of cancers, &c. All these stimuli redden the skin when they are applied to it. 2d. Most of the same stimuli, diminished in intensity, stimulate it but slightly. 3d. Finally, aqueous fluids, cataplasms and emollient fomentations seem to produce this excitement the least; they even rather weaken the cutaneous organic sensibility; they seem to act upon it like sedatives and moderate the kind of excitement it produces in inflammations. The same is true of most of the fatty substances; thus oils, butter, grease, &c. are in general not calculated to keep up the suppuration of blisters. It is requisite, in order to keep the skin at the degree of organic sensibility, necessary for the purulent exudation that then takes place, to mix cantharides with fatty substances.

The skin does not appear to enjoy sensible organic contractility. Stimuli usually produce no other action upon it, than the contraction imperceptible to the eye, which composes insensible contractility, and which takes place especially in the small capillary vessels. There is however one circumstance in which this contraction is, to a certain extent, apparent; it is when cold acts briskly upon the skin, which it wrinkles into goose flesh, as it is called. I have pointed out above the mechanism of this contraction, of which the chorion is the seat, and which holds a medium, like many motions which I have already had occasion to notice, between the two species of organic contractility.

Sympathies.

We shall still follow the division of the sympathies into active and passive, a division which is more remarkable here than in most of the other systems, because the sympathies are much more numerous.

Passive Sympathies.

The animal sensibility is very often brought into action in the skin, by the affections of the other systems. We know that the application of cold to the sole of the foot frequently produces affections of the head; that in many cases, the different species of itching, and even of smarting appear without an injury of the part where the pain is felt. It is useless to cite examples that are known to all physicians. I will confine myself to the sympathies of heat and cold alone, which have not yet been spoken of.

I call by this name the sensation that is experienced upon the skin, when there is not a superabundance or absence of caloric there. There is evidently a material cause for the heat in inflammation and for the cold in the ligature of a great artery. On the contrary, in the cases of which I spoke, it is but an aberration of the internal sensitive principle, which resembles that which takes place when we refer the pain to the extremity of an amputated limb. This is what occurs in many cases of shivering, in which the internal sensitive principle refers to the skin a sensation of which the cause does not exist. By approaching the fire then we do not become warm, because we really were not cold; but we only destroy by a real sensation, the opposite sensation which is illusory that we experience, or rather we turn the perception from this sensation. We know that at the instant of the ejaculation of semen, a sudden and sympathetic chill often extends over the body. We know the cold of fear, which almost always arises, like the sweat produced by this passion, from the sympathetic action exerted upon the cutaneous organ by an epigastric organ affected by the passion.

Observe what takes place in the beginning of most acute local diseases, as in those of the serous and mucous surfaces, of the lungs, of the gastric viscera, &c. &c. The organ which is to be the seat of the disease is at first affected; immediately many sympathetic and irregular symptoms arise in all those which are sound; this is the affection that precedes. When the disease is once developed, and it follows its periods, a new order is established, as it were, in the economy. The relations of the organs seem to change. In the preternatural irregularity of the functions, a kind of regular assemblage of symptoms is manifested, it is this assemblage which characterizes the disease and distinguishes it from every other in which a different order of morbific relations is established between the functions; now the passage from the natural to the preternatural relation of functions is marked by a thousand vague symptoms, which should be attributed to sympathies, and among which appears particularly the kind of shiver in of which I have spoken.

In the beginning of digestion a kind of sympathetic cold is also referred to the skin, which is most often as warm as usual; it is an action exerted by the stomach upon the cutaneous sensibility, an action from which arises a particular sensation, different no doubt from that which the same viscus, when disordered, produces in the head, occasioning head-ache, but which is owing however to the same principle.

The heat is very often sympathetic in the cutaneous organ, less however, as I have observed, than in the mucous system. We know the flushes of heat that so often extend over the skin in an irregular manner, in different fevers, and which are not attended with a greater disengagement of caloric.

Our modern philosophers will not perhaps be able to understand, how it is that whilst in the greatest number of cases, the application of a degree of caloric superior or inferior to that of our temperature, is necessary to produce heat or cold, this sensation can arise in a part though it may not have experienced an increase or diminution of this principle. But in the greatest number of cases has not pain a material cause? And yet all sympathies produce it without this cause. The vulgar, who stop at the diversity of the modifications of feeling, believe that an insulated principle presides over each. Let us disregard all these modifications, in order to see but a single principle in the irregularities as in the regular course of sensibility. That this property, sympathetically altered, gives us the sensation of heat or cold as in the skin, of pulling as in the nerves, of lassitude as in the muscles in the beginning of a disease, &c.; these are but varieties of a single cause, one, of which we are ignorant, but which evidently exists. In general, the sympathies of animal sensibility put into action in each system the sensation which is usual there. The sympathy which, acting upon the skin, creates there a sensation of heat or of cold, would have produced that of lassitude if it had acted upon a muscle.

In order to form an exact idea of heat and cold considered as sensations, let us recollect that they may arise from different causes. 1st. From the increase or diminution of the caloric of the atmosphere. 2d. From the disengagement or the want of disengagement of this fluid in a part of the economy, as in a phlegmon or after the ligature of an artery of a limb. 3d. Sometimes without previous inflammation more caloric is disengaged in the whole body; there is a general increase of temperature; we then feel an internal and external heat; or caloric is disengaged locally in a part of the skin, and the patient feels a heat there as he does who applies his hand upon this place. 4th. Finally, there are sympathies of heat and cold. Some other parts, besides the mucous surfaces and the skin, feel these sympathies; we know the sensation of coldness that is felt to arise from the abdomen to the thorax, &c.

The organic properties of the skin are also frequently put into action by sympathies. The sweat on the skin is suppressed in a moment, if a cold body is taken into the stomach. The entrance of teas into this viscus, and an increased cutaneous exhalation, are two phenomena that take place almost at the same instant; so that we cannot refer the second to the absorption of the drink, then to its passage into the black blood through the lungs, and afterwards into the red blood. The production of sweat is then here analogous to its suppression in the preceding case; it resembles that of fear, and that of phthisis in which the lungs being affected act upon the skin. Shall I speak of the innumerable varieties of this organ in diseases, of its dryness, its moisture, its copious sweats, &c. phenomena for the most part sympathetic, and which arise from the relations which connect this sound organ with the diseased parts? I have pointed out those which exist between it and the mucous surfaces. The membrane of the stomach is the one with which it especially sympathizes. The digestive phenomena are a proof of this. It would be necessary to treat of all diseases in order to speak of the sympathetic influences exerted upon the skin. These influences are often chronic. How in many organic diseases, do different tumours form upon the skin? Precisely as petechiæ, miliary eruptions, &c. are produced in acute fevers; the difference is only in the duration of the sympathetic phenomena.

Animal and sensible organic contractility cannot be evidently put into action in the passive sympathies of the skin, since it is not endowed with these properties.

Active Sympathies.

The four classes of cutaneous affections of which we have spoken, occasion many sympathetic phenomena, the following are some of them.

1st. Whenever the papillæ are strongly excited, as in the tickling of very sensitive people, various organs feel it sympathetically; sometimes it is the heart; hence the syncopes that then take place; sometimes it is the stomach; thus I knew two persons who could be made to vomit by tickling them; sometimes it is the brain, as when in very irritable people, tickling is carried so far as to produce convulsions, which is not very rare in nervous women. Who is ignorant of the influence which the organs of generation receive from the skin, when stimulated in different parts?

Physicians are often astonished at the extraordinary effects which some mountebanks produce in the economy, who know how to profit by their knowledge of the cutaneous sympathies produced by tickling. But why should we be more astonished at these phenomena, than at the vomitings produced by an affection of the womb, at the diseases of the liver arising from an injury of the brain, or at hemicrania the seat of which is in the gastric viscera? The only difference is that we can in the first instance, produce to a certain extent those sympathetic phenomena, which we only observe in the other. Why do we not oftener make use in medicine of the influence which the skin when tickled exerts upon the other organs? In hemiplegia, in adynamic, ataxic fevers, &c. who knows if the excitement of the sole of the foot, which is so sensible, as every one knows, if that of the hypochondrium, which is not less so in some people, &c. would not be better, if repeated ten or twenty times a day, than the application of a blister, the irritation of which soon passes off? Besides you would never obtain by a blister, rubefacients, &c. means which act as much and more upon the organic than the animal sensibility, an effect as striking, an affection as general in the sensitive system, as by the tickling of certain parts, a means, which acting only upon this last species of sensibility, produces phenomena exclusively nervous; whilst the exhalant system and the capillary with red blood are especially affected by the others. Certainly there are cases in which one of these means is preferable to the other. I propose to ascertain these cases.

We have not yet sufficiently analyzed the different kinds of excitement in diseases; we have not endeavoured to profit enough by what observation has taught us, upon the sympathies we can produce at will. Might we not however say, that nature has established certain relations between very remote organs, that we may be able to make use of these relations in our means of cure? The charlatan, who employs external tickling for certain nervous affections, is often more rational, without knowing it, than the physician with all his pharmaceutical means.

2d. Whenever the cutaneous exhalants or the external capillary system from which they arise, are affected in any manner, many other parts feel it, and this is a second order of the active sympathies of the skin. Here are referred a great number of phenomena, of which the following are a part.

A bath which acts upon the skin during digestion, affects sympathetically the stomach, and disturbs this function. When this viscus is agitated by spasmodic motions, oftentimes the influence which it receives from it suddenly calms it, and brings it to its ordinary state. Not long since in my evening visit at the Hôtel Dieu, I saw a woman who was vomiting continually from a sudden suppression of her catamenia. I directed sedatives which were useless. The next evening she was in the same state; I had her put into a bath; every thing was calmed the moment she came out of it, and yet the catamenia did not return. Few organs are more dependant on the skin than the stomach.

The action of cold upon the cutaneous organ produces many sympathetic effects, especially when this action takes place while we are sweating. The term repercussion of transpiration is not proper to express what then takes place; it gives a very inaccurate idea. Let us suppose that a pleurisy arises from cold suddenly applied, the following is what happens; the organic sensibility of the skin being immediately altered, that of the pleura is sympathetically altered. By it the exhalants become in relation with the blood; they admit it instead of the serum which they before received, and inflammation supervenes. Thus this phenomenon is the same as that in which the application of a cold body upon the skin suddenly arrests uterine, nasal hemorrhage, &c. &c.; the result only differs. Now in this last case, no one ever supposed that there was a repercussion of fluid. The suppression of the transpiration is a thing purely accessory and foreign to the internal inflammation which takes place. When the skin sweats in summer, the vital forces are more raised by the caloric which penetrates it; in this state, it is more capable of acting sympathetically upon the forces of the other systems. Hence why all strong stimulants that act upon it are more to be feared then. It is so true that it is not the suppression of the sweat which is dangerous, but the alteration of the vital forces of the skin which sweats, that many kinds, as the sweat of phthisis, are not so injurious when they cease for a time; they are checked even with much more difficulty, because they are not produced by a cause acting immediately upon the skin. Now if there was a repercussion of the transpiration, every species of sweat that was suppressed would be injurious. We never hear of a peripneumony arising from a suppression of sweat produced by fear, rheumatism, &c. There would be then also a repercussion of mucous matter, when a pleurisy arises from swallowing a glass of cold water. Men judge only by that which is striking. The suppression of the sweat is an effect like inflammation of the pleura, but it is not the cause of it. If there was no sweat the instant the cold was applied to the skin, inflammation would nevertheless come on. In wounds of the head, with abscesses of the liver, &c. there is no repercussion of fluids.

The trembling of which the voluntary muscles become the seat, the debility of the pulse which the weakness of the action of the heart produces, &c. are phenomena which the influence of the skin affected by cold alone causes. In fact, only this organ, the commencement of the mucous surfaces and all of that of the bronchia, are made cold by the external air; all the others remain at their usual temperature.

We know the innumerable phenomena which arise from the disappearance of herpes, the itch, &c. imprudently produced; in all these cases it does not appear that the morbific matter is carried to the other organs, though I do not pretend that this never happens. It is the vital forces of these which are raised and which then occasion different accidents; now as these forces vary in each system, these accidents will be essentially different; thus the same morbific cause disappearing from the skin, will produce vomiting if thrown upon the stomach, in which the sensible organic contractility predominates; pains, if it goes to the nerves which are especially characterized by animal sensibility; derangements of sight, hearing and smell, if it affects the respective viscera of these senses; hemorrhage, catarrhs, phthisis, tubercular inflammation, &c. if it attacks the mucous surfaces, the lungs, the serous membranes, &c. in which the organic sensibility is much raised. Now, if the same morbific matter carried upon these different organs, produced these accidents, they ought to be uniform. Do not their varieties, and especially the constant analogy which they have with the predominant vital forces of the organs in which they appear, prove, that they depend upon the cause which I have pointed out?

We know that the serous surfaces and the cellular texture on the one part, and the skin on the other, are often in opposition in diseases. There is no sweat when dropsies are formed; the dryness of the skin is often even more remarkable than the small quantity of urine, &c.

3d. When the cellular texture contained in the dermoid spaces is inflamed, as in phlegmonous inflammation, in biles, in some malignant pustules, &c. there comes on many sympathies which can be referred to those of the general cellular system, which have been already noticed.

4th. The affections of the chorion itself, all marked with a chronic character, on account of the kind of vitality and structure of this portion of the skin, occasion also sympathies which have the same chronic character, but of which we know but little.

The organic contractility cannot be put sympathetically in action in the skin, as it does not exist there.

Characters of the Vital Properties. First Character. The Cutaneous Life varies in each organ.

Though we have spoken in general of the vital properties of the skin, they are far from being uniform or at the same degree in all the regions.

1st. There is no doubt that the animal sensibility of the soles of the feet and the palms of the hands is greater than that of the other parts. Many persons are so sensible in the hypochondriac region, that the least tickling there produces convulsions. The anterior and lateral part of the trunk is always more sensible than the region of the back.

2d. The organic properties do not vary less. The extreme susceptibility of the face to receive the blood, is a proof of it, as I have said. It is generally known that some parts are more proper than others for the application of blisters. Observe on this subject that the places where the animal sensibility predominates, are not the same as those in which the organic is in the greatest proportion. The soles of the feet and the palms of the hands hold the first rank in relation to one, and the face in relation to the other.

In diseases we also see these varieties. Who does not know that some particular parts of the skin are especially the seat of some particular cutaneous affections, and that when these affections are general, they always predominate in certain places. We ought not to be astonished at these varieties, since we have seen that the dermoid texture is infinitely variable as it respects its papillæ, its reticular body, its chorion, &c.

Second Character. Intermission in one relation; continuity in another.

The life of the cutaneous system is essentially intermittent in relation to animal sensibility. All the senses exhibit this phenomenon. Thus when the eye has for a long time gazed upon objects, the ear heard sounds, the nose received odours, and the mouth tastes, these different organs become unfit to receive new sensations; they become fatigued, and require rest to regain their forces. It is the same with regard to feeling and the touch; wearied by the impression of surrounding bodies, the skin requires an intermission of action to regain excitability adapted to new impressions. We know that a short time before sleep, external bodies produce but an obscure sensation upon it, and that their contact has no effect in this state, in which animals seem to lose half of their existence. The more powerfully the cutaneous sensibility has been excited, the more profound is sleep; hence why all painful exercises, great frictions, &c. are always followed by a deep sleep. Yet this sense can sometimes exert itself, while the others sleep; pinch the leg of a man asleep; he draws it away without waking, and has afterwards no remembrance of the sensation. Thus somnambulists often hear sounds, even eat, &c.; for, as I have said elsewhere, sleep may affect but a very limited part of animal life, as it may the whole.

Under the relation of organic sensibility, the life of the cutaneous system is essentially continuous. Thus the functions over which this property presides have a character opposite to the preceding. The insensible transpiration takes place continually, though there may be some periods in which it is more active than in others. The oily fluid is incessantly carried away and renewed; we might even say sometimes that it is when the animal sensibility is interrupted, that the organic is in the greatest exercise.

It is especially in diseases that they have made this observation, which is besides generally applicable to organic life. All this life is as active and even more so during the night than during the day. Most of the diseases that attack the functions which belong to it, are marked by an increase of activity during the night. All fevers which particularly affect the circulation have their exacerbation towards night. In diseases of the heart, the patients are more oppressed at this period, &c. In phthisis which affects respiration, it is in the night especially that there is hectic fever, sweats, &c. Pneumonia and pleurisy, exhibit frequent exacerbations towards night. In glandular diseases, either acute or chronic we make the same observation. It would be necessary to refer to almost all the affections which alter especially an organic function, in order to omit nothing upon this point. On the contrary, observe hemiplegia, epilepsy, convulsions, various paralysies of the different organs of sense, most mental alienations, apoplexy and other affections which exert their influence more particularly upon animal life, they have not, so often at least, their exacerbations towards evening and during the night, no doubt because in the natural state, this life is in the habit of becoming drowsy and not of being raised like the other which seems to imprint this character upon its alterations. Other causes no doubt have an influence upon this phenomenon; but I believe this to be a real one.

Third Character. Influence of the Sexes.

The sex has an influence upon the cutaneous life. In general the animal portion of this life is more raised in women, in whom every thing that belongs to the sensations is proportionally more marked than in man, who predominates by the power of his locomotive muscles. The effects of tickling are infinitely more powerful in females. All the arts which require nicety and delicacy of touch are advantageously cultivated by women. The peculiar texture of the chorion, a texture generally more delicate, has no doubt an influence upon this phenomenon. As to the organic portion of the cutaneous life, the difference is not very great. Man appears to be superior in this respect; he generally sweats more; his skin is more unctuous, which proves a greater secretion.

Fourth Character. Influence of Temperament.

The temperament peculiar to each individual is not a less real cause of differences in the skin. We know that the colour, roughness and pliability of this organ vary according as individuals are sanguineous, phlegmatic, &c. that these external attributes are even a character of the temperaments. Varieties of structure no doubt coincide with these. Is it then astonishing that the animal sensibility differs so much, that the touch itself should be delicate in some and dull in others, that some should be very ticklish, whilst others are not so at all, &c.? Ought we to be astonished if the organic sensibility, which is very variable, should determine, according to the individuals, many varieties in the phenomena over which it presides; if in some, it allows much blood to go to the face, and if it repels this fluid in others who are always pale; if some men sweat much, whilst others have the skin almost always dry; if the cutaneous oil varies in quantity; if there are some skins much disposed to eruptions, either acute or chronic, to pimples of different natures, and if others are almost always free from them, even when the individuals expose themselves to the contagion of these diseases; if superficial wounds, of the same extent and made by the same instrument, are sometimes quicker and sometimes slower in healing; if the cure of cutaneous diseases is also very variable in its periods, &c. &c.?

ARTICLE FOURTH. DEVELOPMENT OF THE DERMOID SYSTEM.

I. State of this System in the Fœtus.

In the first periods after conception, the skin is but a kind of glutinous covering, which seems to be gradually condensed, forms a transparent envelope, through which we see in part the subjacent organs, the vessels especially, and which is torn by the least jar. This state continues for a month and a half or two months. The consistence constantly increasing, soon gives to the skin an appearance more nearly like that which it has in infants after birth. Its delicacy is extreme at this period. It has not one quarter the thickness of that of the adult. The moment in which it begins to lose its mucous state appears to be that in which the fibres of the chorion are formed. Until then the cellular texture and the vessels especially composed it, and as the first is abundantly filled with juices during the early periods, it is not astonishing that it should then give way under the least pressure. But when the fibres are formed, the cellular texture diminishes on the one hand, and is concentrated in the spaces that are developed, and on the other the dermoid fibres, more dense than its layers, increase the resistance.

We do not see upon the external surface of the skin of the fœtus most of the wrinkles of which we have spoken above. Those of the face in particular are not seen; the kind of immobility, in which the facial muscles are, is evidently the reason of it. The forehead, the eyelids, the edges of the lips, &c. are smooth. Besides, the abundance of fat which then distends the integuments of the cheeks, prevents every species of fold there. As the hands and the feet are found in part bent at their articulations, by the attitude of the fœtus, different wrinkles are already formed about these articulations, principally on the hand, where however they appear less in proportion than afterwards. The curved, papillary lines are not very evident on the foot and the hand, even when the epidermis is removed.

The internal surface of the skin is remarkable for the slight adhesion of the subjacent cellular texture, the cells of which filled with fatty particles are removed with great ease, by scraping this surface with the edge of a knife. We see then there the spaces already well formed, and as distinct in proportion as afterwards. By pursuing their dissection from within outwards, we insensibly lose sight of them towards the external surface where the skin is condensed.

More blood enters the skin of the fœtus, than at any other period of life. It is easy to observe this in small animals taken alive from the womb of their mother; for in the fœtuses that are dead at birth, or born prematurely, the cause which destroys life, increasing or diminishing in the last moments the quantity of cutaneous blood, prevents us from drawing any conclusion as to the ordinary state by an inspection of them. The nerves are, as in all the other parts, more evident; but the papillæ, though sensible, as I have said, have not a proportionable increase.

The animal sensibility is not in exercise in the skin of the fœtus, or at least it is very obscure there. This is owing to the absence of the causes of excitement. These are the surrounding heat, the waters of the amnios and the parietes of the womb, which can furnish materials for sensations; but as these causes are always uniform, and have no varieties, the fœtus can have but a very feeble perception, because acuteness of sensation requires change of stimuli. We know that heat long continued at the same degree becomes insensible, that a long continuance in a bath takes away almost entirely the sensation of the water, because habit is every thing as it respects sensation; nothing but what is new affects us powerfully.

Is the organic sensibility of the skin in activity in the fœtus? does it preside over the alternate exhalation and absorption of the waters of the amnios? This is not the common opinion, it is not even a probable one; but this question is far from being settled in so precise a manner as many other points of physiology.

Besides, it cannot be doubted that there is a copious secretion of an unctuous and viscid fluid, which covers the whole body of the fœtus, but which is more abundant in some places than others, as behind the ears, in the groin, the axilla, &c. either because it is secreted there in greater quantity, or accumulated on account of the arrangement of the parts. Accoucheurs have it wiped off after birth, and the females of animals remove it by the repeated application of their tongues to the surface of the body. This fluid appears to be to the skin of the fœtus what the oily fluid is to that of the adult; it defends this organ from the impression of the waters of the amnios. If the sebaceous glands exist, it would appear that they furnish it, for it is certainly from a different source from the sweat. When care has not been taken to remove this covering, it irritates the skin, and may produce excoriations, and a species of erysipelas. The air cannot remove it by solution. Nothing similar oozes from the skin of the infant after birth. Is it because the black blood alone is capable of furnishing the materials of this substance?

II. State of the Dermoid System during growth.

At the moment of birth the dermis experiences a sudden revolution. Hitherto entered only by black blood, it is at the time the fœtus is born, more or less coloured by it. Some fœtuses come wholly livid, others are paler; there is a remarkable variety in this respect. But all, shortly after they have respired, become more or less decidedly red. It is owing to the arterial blood which is formed and succeeds the venous blood that circulated in the cutaneous arteries. In this respect the state of the skin is in general an index of what goes on in the lungs. If an infant remains a long time of a violet colour, he either does not breathe or breathes with difficulty. The extremities of the hands and the feet in general become red the last. They are those in which the lividity consequently continues the longest, when this lividity is very evident. The blood which goes to the cutaneous organ, enters it in general in a very uniform manner; the cheeks do not appear to receive more of it in proportion. The sudden excitement it brings to the organ, raises its vital forces and renders it more fit to receive the impressions, which are new to it, of the surrounding bodies.

Observe in fact that a thousand different agents, the surrounding temperature, the air, dress, the fluid in which the fœtus is washed, the tongues of those quadrupeds who lick their young, carry to the skin an excitement which is so much the more felt by the fœtus, as it is not accustomed to it, and as there is an essential difference between these stimuli, and those to which it had been previously subjected. It is then that the remarkable sympathy which connects the skin with all the other organs, becomes especially necessary. Every thing within soon perceives the new excitements that are applied without. It is these excitements, those of the mucous surfaces at their origin and those of the whole of the bronchia, which especially bring into action many organs hitherto inactive. There happens then, what is observed in syncope, in which respiration, circulation, the cerebral action and many functions suspended by the affection, are suddenly roused up by external friction, by the irritation of the pituitary membrane, &c. The phenomena are different, but the principles from which they are derived in both cases are the same.

Then the organic sensibility is also raised. Transpiration is established. The skin begins to be an emunctory of different substances, which it did not before throw out; it becomes also capable of absorbing different principles applied to its surface. The skin of the fœtus is hardly ever the seat of any kind of eruptions; then pimples of different kinds frequently appear.

All the parts of the cutaneous organ do not however appear to be raised to the same degree of organic sensibility. For a long time after birth the skin of the cranium appears to be the centre of a more active life; it becomes the frequent seat of many eruptions, all of which denote an excess of the vital forces. The different kinds of scurf with which it is covered do not appear elsewhere. In this respect, the skin of the cranium follows, like the bones of this part and the cerebral membranes, the early development of the brain, which, on this account is the seat of diseases in infancy more than at any other age.

The skin of the face seems to be sometimes in less activity. In the first months after birth, it has not that bright colour which it will afterwards have upon the cheeks, and which does not commence until the development of the sinuses and dentition bring to this part more vital activity for the nutritive work. It is also towards this period that the eruptions of which this part of the cutaneous system is especially the seat, like those of the small-pox, measles, &c. begin to take place.

For a long time after birth the skin still preserves a remarkable degree of softness; a very great quantity of gelatine enters it; this substance is obtained from it with great ease by ebullition, which, continued for some time, finally melts this organ entirely. The fibrous part noticed by Seguin, is in very small quantity. I think it is this predominance of the gelatinous portion of the skin, which renders that of young animals easy of digestion. We know that in calves’ heads, roasted lamb, and small sucking pigs, prepared for our tables, it presents an aliment which the digestive juices alter with the greatest ease; whilst that of animals of mature age and especially old ones, cannot be digested by them. The carnivorous species tear their prey, feed upon its internal organs, the muscles especially, and leave the skin. Now what is it that makes the skin of young animals differ from that of old ones? It is because the gelatinous substance predominates over the fibrous in the first, and the fibrous predominates in the second.

The skin of children is gradually thickened; but it is not until the thirtieth year that it acquires the thickness that it is always to have afterwards. Till then the different ages are marked in this respect by different degrees. Take a portion of skin at birth, at two, six, ten, fifteen, twenty years, &c. you will see these differences in a remarkable manner. The more its thickness increases the more compact it becomes; it is because the fibrous substance tends constantly to predominate over the gelatinous.

As we advance in age, the adhesion of the internal surface of the dermis with the subjacent cellular texture becomes much greater. It is more difficult to detach one from the other. On the external surface the wrinkles of the face are gradually formed. Smiles and tears agitate the face of the infant the most. One is the expression of the happiness, the other of the uneasiness which all its passions produce in its mind. Now the wrinkles which weeping occasions on the eyelids are marked in rather a more permanent manner, either because weeping is more frequent than smiling, or because continual winking adds to the motion which weeping produces, or because less fat is found in this place. As smiling is on the one hand more rare, and on the other much fat puffs out the cheeks of the infant, the perpendicular wrinkles formed by the muscles of the face, which in this motion separate transversely the features from within outwards, are much slower in forming. Besides, the nursing of the infant, which requires the contraction of its face from without inwards, opposes their formation. The wrinkles of the forehead are always very slow in forming, because the motions which contract the eyebrow, and those which wrinkle the forehead, are rare in the infant, who has hardly any of those dark passions which these motions serve to depict.

The growth of the dermoid system has not remarkable revolutions like that of most of the others; it goes on in an uniform manner. At the period of the growth of the hairs, it does not change, because this growth is absolutely foreign to it, these productions only passing through it. At puberty it increases in energy like all the other systems. Until then sweats had not been very copious; for, other things being equal, we may say that children sweat less in general than adults, and that the residue of their nutrition passes rather by the urine, which is probably the reason why they are so remarkably disposed to calculi. Beyond the twentieth year we begin to sweat more, and until old age, especially in summer, the fluids appear to go out in this way.

III. State of the Dermoid System after Growth.

After growth, the skin continues for a long time to have great activity; the excess of life which animates it, renders it capable of influencing with ease the other organs if it be but a little excited. Hence the disposition to pneumonia, pleurisy, &c. from the action of cold on the skin in sweat, a state in which it is more disposed to exert an injurious influence upon the internal organs, because its forces are more excited. As to the different affections which result from this influence, they depend upon the internal organs upon which it is directed; so that the same sympathetic irradiations going from the skin, will produce sometimes an affection of the abdomen, sometimes a disease of the thorax, according to the age in which the abdominal or pectoral organs, predominating by their vitality, are more disposed to answer to the influence directed in general upon the whole economy.

The skin becomes more and more firm and resisting as we advance in age, as the fibrous substance is constantly tending to a predominance over the gelatinous. Less blood seems to be carried to it. It becomes less and less disposed to eruptions, so common in youth and infancy, &c. I will not speak of its other differences; for all that we have said of it in the preceding articles relates especially to the adult age.

I will only observe that if, during the greatest part of life, the skin be so fruitful a source of diseases, and the various alterations it experiences produce so frequent disorders in the internal organs, it is only owing to the varied causes of excitement to which it is every instant subjected. If the glands, the serous surfaces, &c. have an influence less frequently upon the other organs, it is because being deeply situated, and almost always in contact with the same excitants, they are not subject to so many revolutions in their vital forces. The secreted fluids and those exhaled in the serous and synovial systems are not, for the same reason, so much subject to those considerable increases, and those sudden suppressions which so frequently happen to the sweat.

Observe that society has also multiplied to a great extent the injurious excitements to which the skin is subjected. These excitements consist especially in the rapid passage from heat to cold, which makes the latter act very powerfully upon the cutaneous sensibility, which like that of all the other systems, answers so much the more to excitements made upon it, as they are different from those, whose action they had previously experienced. In the natural state, there is only the succession of the seasons; nature knows how to connect insensibly heat with cold, and to make the transition but rarely abrupt. But in society, the different garments, the artificial degrees of temperature of our apartments, degrees differing at first from that of the atmosphere, then varying greatly from each other, so that the same man who in winter enters thirty apartments, is often subjected to thirty different temperatures; the hard labour in which most men are engaged, and which makes them sweat copiously, every thing incessantly presents numerous causes which make the vital forces of the dermoid system vary rapidly. Thus the bronchial mucous surface is constantly in contact in cities, with a thousand excitements that are continually renewed, and with which the air is not charged in a natural state. Thus the alimentary substances, continually varying in their composition, temperature, &c. change the excitement of the gastric mucous surface, and are the source of many affections, from which most animals are exempt by the uniformity of their food.

If the skin and the mucous surfaces were always kept at the same degree of excitement by the constant uniformity of the stimuli, they would certainly be a much less fruitful source of diseases, as is clearly proved by the fœtus, which is hardly ever sick, because all the external causes which act upon its mucous and cutaneous sensibility, as the heat, the waters of the amnios and the parietes of the womb, do not vary until birth. At this period, animals brought into a new medium, find many more varieties in the stimuli which act upon them, even in a natural state and far from society; thus their diseases are naturally much more frequent after than before birth. In society, in which man has increased four, six and even ten times the number of the stimuli which affect the surfaces destined to be in contact with the external bodies, is it astonishing that the diseases should be so disproportioned to those of animals?

IV. State of the Dermoid System in Old Age.

Towards the decline of life, the dermoid system becomes more and more firm and compact; it is softened with great difficulty by ebullition. The gelatine, which it yields, is less abundant and more hard and consistent. I think it would not be fit to make any kind of glue, even the strongest, unless mixed with that of adult animals. Its yellowish tinge becomes very deep. When it is cooled, it requires a much stronger and more durable fire to melt it; the fibrous portion of the dermis which does not melt or at least resists for a long time, is infinitely greater in proportion. It is like the bones in which the gelatinous portion is in an inverse ratio, and the earthy portion in a direct ratio to the age.

The dermoid texture becomes then like all the others, dense and stiff; it is not proper for our food, the teeth cannot tear it. Prepared with tannin, it is more resisting and less pliable, and cannot on that account serve for the same purposes as that taken from young animals. Every one knows the difference of the leather of calves and oxen, especially when the latter are old. This difference is owing first to the thickness, which being much greater in the second than the first, does not allow it to be so easily bent in different directions; and then to the nature of the texture itself. Cut in two horizontally a piece of the leather of an ox; each half will be as thin as a piece of calves skin, and yet it will be less pliable. I do not estimate here the varieties which may depend on the greater or less quantity of tannin that may be combined with it; I suppose the proportions to be all equal.

Submitted to desiccation, the human dermoid texture becomes much more stiff in old age than in the preceding ones. Maceration softens it with more difficulty. The hair of a child falls out much sooner by it than that of an old person; thus it requires longer to clean the skins of old animals than those of young ones; tanners know this very well. I would remark upon this subject, that the skins of animals, having more hairs pass through them, exhibit in comparison with that of man, an innumerable quantity of little pores on their external surface; which favours in them on this surface the action of tannin, which insinuating itself into the dermoid spaces and filling them completely with a new substance formed by the combination of tannin with gelatine, occupies entirely the texture of the spaces. The previous maceration to which the skin has been exposed, favours not only the removal of the hairs, but facilitates also to a great degree the entrance of the tannin, by separating the fibres of the spaces, by making them larger, and increasing the size of the external pores.

The more we advance in age, the less is the quantity of blood that penetrates the skin. The redness of the cheeks disappears in old people. We no longer see then the rosy complexion of the young man and even of the adult, and which arose from the vessels winding through the cellular texture of the spaces of the chorion.

The continual pressure of external objects increases then remarkably the adhesion of the subjacent cellular texture to the dermis. They are separated from each other with great difficulty by carrying the edge of a scalpel over the internal face of the chorion; a circumstance which is owing also to this, that the cellular texture having become more dense, is less easily torn; for this tearing is then necessary, considering the continuity of the sub-dermoid layer with that which enters the spaces. The exterior of the skin is uneven and rough. All the wrinkles of which we have spoken become infinitely more evident; many belong exclusively to this age.

The vital forces of the dermoid system are more weakened in old age than those of most of the others, because it is more excited during life by external bodies. Most of these bodies then make no impression upon it. The habit of feeling has blunted the animal sensibility. The touch is exercised but rarely; for, as I have observed, this sense requires to put it in action, the previous exercise of the will. We touch, because we have previously seen, heard, tasted, &c. in order to correct or confirm our other sensations; now the old man, to whom every thing around is known, to whom nothing is new, is induced to touch nothing. Compare in this respect the two extreme ages of life. The infant, to whom every thing that strikes his eyes, his ears, his nostrils, &c. is unknown, who finds in every thing that surrounds him new objects of sensation, wishes to touch and lay hold of every thing. Its little hands are in continual agitation. To touch is a pleasure to him, for every new object of sensation is agreeable. If in his last years, man was transported into the midst of objects that never before struck his senses, he would oftener exercise his touch; but none of those things excite him among which he has always lived. Hence why old age is not the age of enjoyments. In fact all our pleasures are almost relative; we have but little that is absolute; now as habit blunts all the relative pleasures, which cease because they have existed, the more the sensations are accumulated by time, the less there are of new ones left to be experienced, and the more are the sources of happiness dried up. For a contrary reason, the happiest age is infancy, because it has before it the whole field of sensations to go over. Man at every step of his career leaves behind him a cause of his enjoyments. When arrived at the end he finds only indifference, a state very suitable to his situation, since it diminishes the distance that separates life from death.

The organic sensibility of the skin is not less blunted in old age, than its animal sensibility; hence the following phenomena; 1st, contagious miasmata are absorbed with difficulty at this age; almost all pass over the cutaneous surface with impunity. 2d. The exhalation of sweat is uniformly less; it is hardly ever subject to those great increases, that are seen in the adult. 3d. The oily fluid is also furnished in much less quantity; hence the constant dryness of the exterior of the skin, the cracking of the epidermis in some cases, &c. 4th. All the diseases which suppose an increase of this organic sensibility are much more rare. Erysipelas and the different kinds of eruptions are a proof of it. When these affections take place, they have a character of remarkable slowness. 5th. The skin resists external cold much less; it loses easily the caloric of the body, which always tends to escape in order to be in equilibrium with that of the surrounding medium; thus old people are always fond of heat. 6th. I am well persuaded that the skin would resist also less, at this age, a degree of temperature greater than that of the body, and as it permits the internal caloric to be easily lost in a colder medium, it would allow the external to penetrate in a warmer one. It would be very curious to repeat, on the two extreme ages of life, the experiments of the English physicians.