Chapter XII: Part 12

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.