All animals are covered with a more or less compact membrane, of a thickness in general proportioned to the size of their body, destined to defend the subjacent parts, to carry out a considerable portion of the residue of nutrition and digestion, and to place it in relation with external bodies. It is in man a sensitive boundary, placed at the extremity of the domain of his mind, where these bodies continually touch, for the purpose of establishing the relations of his animal life, and of thus connecting his existence with that of every thing which surrounds him. This covering is the dermis or skin. We shall call the whole of it the Dermoid System.
ARTICLE FIRST.
FORMS OF THE DERMOID SYSTEM.
The covering which forms this system, being proportioned to the parts that it covers, is applied to these parts, adapted to their great inequalities, and allows the largest external prominences to be visible, but conceals a great number on account of their small size; thus the appearance of the body stripped of skin differs very much from that with the skin on.
This covering everywhere continuous is reflected through different openings in the interior of the body and goes to give origin to the mucous system. The limits between the two systems are always marked by a reddish line; within this line is the mucous system, without it the dermoid. Yet the demarcation is not as striking in the organization as in the colour. Both are confounded in an insensible manner. In the neighbourhood of these openings, of those of the face especially, the dermoid becomes more delicate. At the commencement of these openings, the mucous borrows more or less, as I have said, the characters of the first.
I. External Surface of the Dermoid System.
This surface, everywhere contiguous to the epidermis, is remarkable for the hairs which cover it, for the oily fluid which constantly lubricates it, for the sweat that is deposited on it, for the sense of feeling of which it is the seat and which the internal surface does not possess. We shall in this article consider only the external dermoid forms, without regard to these different objects.
We see upon this surface different kinds of folds.
1st. Some are owing to the subjacent muscles which, being intimately connected with the dermis, forming almost a part of it, wrinkle it when they contract. Such are the wrinkles on the forehead; those in the form of rays which the orbicularis produces around the eye-lids, &c.; those of which the cheeks are the seat, when the great and small zygomatic, &c. contract; those which the orbicularis of the lips produces around the mouth, when it contracts it by diminishing its opening, &c. All these folds are owing to this, that on the one hand the skin cannot contract like the muscles, and that on the other it is necessary that it should occupy less space in length at the instant these are shortened. They are of the same nature as those of which the mucous surfaces, that of the stomach in particular, become the seat in the contraction of the fleshy layer which is contiguous to them. Thus the direction of these folds is always perpendicular to that of the subjacent muscles whose fibres they cut at a right angle. We are accustomed to attach much importance to the existence of these wrinkles in the expression of the passions; no doubt because then they are strongly marked. In fact the breadth of the face of man makes it well adapted to their development, whilst that of animals is badly formed to produce them. Thus their eye, rather than the features of the face, is the moveable picture which is differently sketched at every instant by the various feelings of anger, hatred, jealousy, &c. The wrinkles of the human face contribute very much to the expression of the countenance, they compose in part the physiognomy, and mark its different shades.
The wrinkles of the scrotum are analogous to these; they depend upon the contraction of the subjacent cellular texture, in which some fleshy fibres appear also to exist.
2d. There are other wrinkles which are owing also to the motions, but not to those of the subjacent muscles. There are those of the sole of the foot, and especially those of the palm of the hand. There is not there any sub-cutaneous muscle adhering to the skin, except the small palmar muscle, which has no agency in these wrinkles that are formed at the places where the skin is constantly folded in flexion. Thus there are many of them about all the articulations of the phalanges. In the palm of the hand, we see three principal ones, one at the base of the thumb, produced by the motion of opposition, another at the anterior part of the palm, occasioned by the flexion of the four last phalanges which are bent towards the thumb, and the third is found in the middle of the palm. The dermis is folded between these depressed lines, in the motions in which the hand is hollowed. Many other small folds corresponding with less evident and less frequent motions, cut these at different angles.
On the back of the foot and hand, there are many wrinkles about each articulation of the phalanges, when they are extended. They disappear in flexion, and are owing to this, that nature, on account of the motions, has made the skin more loose at this place, and broader in proportion to the parts it covers. About most of the articulations, there are analogous folds, but they are much less evident, because the skin adheres less to the neighbouring parts. Upon the whole trunk, the arm, the fore-arm, the thigh and the leg, we see no depressions but those from the muscular prominences.
3d. There is a third species of wrinkles, or rather cutaneous impressions, which are not very evident, found especially on the sole of the foot and the palm of the hand and which we easily distinguish from the preceding; they are those which indicate the rows of the papillÆ. The surface of the trunk presents hardly any thing similar.
4th. Finally, there are the wrinkles of old age, which are of a wholly different nature. The sub-cutaneous fat having in part disappeared, the skin becomes too large for the parts it covers; now as it has lost with age its contractility of texture, it does not contract, but folds in various directions. Thus where there was the most fat, as on the face, these wrinkles are the most evident, they resemble those that appear on the abdomen after several pregnancies, dropsy, &c. In young people, if emaciation takes place suddenly, the skin contracts, and no wrinkle is formed.
II. Internal Surface of the Dermoid System.
This surface answers everywhere to the cellular texture which is loose upon the trunk, the thighs, the arms, &c. and which is condensed upon the cranium, the hand, &c. In most animals, a fleshy layer called panniculus, and of a form analogous to that which is almost everywhere subjacent to the mucous system of man, separates the skin from the other parts, and communicates to it various motions. In man, the dermoid system exhibits here and there traces of this internal muscle, as is observed in the platysma myoides, the occipito-frontalis and most of the muscles of the face. There is nothing similar on the trunk, extremities, &c. Man is as much inferior in this respect to most animals, as he is superior by the arrangement of his facial muscles. Thus observe that whilst in him all the passions are painted as it were upon the face, and the whole exterior of the trunk remains calm in these tempests of the mind, this exterior is convulsively agitated in animals. The mane of the lion becomes erect, the whole skin of the horse moves, a thousand different agitations animate the exterior of the trunk of animals, and make it a general picture on which is painted all that passes in the interior. You can determine from behind, in many animals, by seeing only their bodies, that they are agitated with passion; cover the face of man, the curtain is drawn over the mirror of his mind; thus almost all nations leave it uncovered. The physiognomy is in this respect, if we may so say, more generally spread over the exterior, in animals with a fleshy panniculus.
Besides the cellular texture, the dermis is almost everywhere subjacent to the muscles in the trunk; but, foreign to the motions of these muscles, it receives no sensible influence from them. In the extremities it is found separated from the fleshy layers by aponeurotic expansions. Many vessels wind under it; the great veins pass through its texture; many arterial ramifications go upon its surface, and many nerves between these ramifications.
ARTICLE SECOND.
ORGANIZATION OF THE DERMOID SYSTEM.
I. Texture peculiar to this Organization.
This texture comprehends, 1st, the chorion; 2d, that which is called the reticular body; 3d, the papillÆ. The chorion is the essential part of the dermis; it is that which determines its thickness and form. The reticular body appears to be but little distinct from it. The papillÆ arise from it also, but are more evident.
Chorion.
The chorion is of a very variable thickness. 1st. In the head, that of the cranium and that of the face exhibit an opposite arrangement. The first is very thick and also dense and compact, which is owing especially to the numerous hairs that go through it. The second, everywhere fine and delicate, is particularly so upon the eyelids and the lips. 2d. The chorion of the trunk is posteriorly and all along the back, of a thickness almost double that of its anterior part, where it is nearly the same upon the neck, the chest and the abdomen. I would except however that of the penis, the scrotum, the great labia and the mammÆ, in which its delicacy is greater than any where else. 3d. In the superior extremities it is nearly uniform upon the shoulders, the arm and the fore-arm; on the hand it increases a little in thickness and more in the palm than on the back. 4th. This thickness is generally much more evident on the thigh and the leg, where there are more muscles, than on the arm or the fore-arm. On the foot, it increases as on the hand, less in the dorsal than in the plantar region, which is the thickest of all the parts of the dermoid system; which is owing principally in the natural state to the arrangement of its epidermis. We see from this, that though everywhere continuous, the chorion is very different in its different parts. The relation of its thickness with its functions is easily perceived on the hand, the foot, the cranium, &c. Elsewhere we cannot so well see the reason of these differences, which are notwithstanding as constant.
Woman has a chorion generally less thick than that of man; compared in all the regions, it exhibits in the two sexes a sensible difference; on the mammÆ especially, it is much more delicate in woman. That of the great labia however is proportionally thicker than that of the scrotum.
In order to understand perfectly the intimate structure of the chorion, it is necessary to examine it at first on its internal surface, after having carefully separated it from the fatty cellular texture, to which this surface adheres more or less intimately. We see then that it is differently arranged according to the regions.
1st. On the sole of the foot and the palm of the hand, we observe an infinite number of white fibres, shining like aponeurotic fibres, which are detached from this internal surface, form upon it a kind of new layer, cross each other in all directions, leave between them, especially towards the heel many spaces of different sizes, that are filled with fat, separate more and more, and are finally lost in the sub-cutaneous texture, nearly as the fibres of the brachial aponeurosis insensibly disappear in the neighbouring cellular texture. Hence why when we dissect the palmar and plantar integuments, we experience the greatest difficulty in separating them entirely from the cellular texture which is interlaced with these fibres; hence why also these surfaces have not, on the parts which they cover, the mobility which many others exhibit.
The density of the cellular texture contributes also something to this arrangement which is essential to the functions of the foot and the hand, which are designed to seize and grasp external bodies.
2d. The dermis of the superior and inferior extremities of the back, of the neck, of the thorax, of the abdomen, of the face even and consequently of almost all the body, is distinguished from the preceding, because the fibres are much less distinct, and are not lost in the cellular texture by being as it were confounded with it, whence arises a remarkable laxity of the skin of these parts, and the very great facility with which it is dissected; in a word because the spaces between these fibres are much more narrow. These spaces appear like an infinite number of holes irregularly placed at the side of each other, containing most of them small fatty parcels of the neighbouring texture, and exhibiting, when these small parcels have been carefully removed, very evident vacuities. The fibres which form them, are sufficiently near each other, to make you believe at first view, that it is a surface pierced with an infinite number of holes, that has been applied under the skin. On the contrary, on the hand and the foot, towards the heel especially, it is a true net-work the spaces of which are larger than the fibres that form them; this is the reverse here. Be that as it may, these spaces in the internal surface of the chorion are very favourable to the action of tannin which penetrates the texture infinitely better from this side than from the opposite, because it insinuates itself into these numerous openings. I have had occasion to observe it in the human chorion which I have had tanned for the purpose. Chaptal has observed that the epidermis is a real obstacle to the action of tannin, and that on this account scraping is a preliminary operation essential to tanning, since it allows the skin to be penetrated on both sides; but even when thus scraped, it receives the tannin much more easily on the side of the flesh than on the opposite one.
3d. The chorion of the back of the hand and the foot, as well as that of the forehead does not exhibit these numerous openings on its internal surface; it is smooth and white, especially when it has been macerated a little. It is precisely the same as that of the scrotum, the prepuce and even the great labia. The texture of it is more compact, no space is left in it, so that though more delicate than that of the extremities and the trunk, it contains almost as much substance. As to the chorion corresponding to the hair and the beard, we see in it only the openings necessary for the passage of the hairs, and which are wholly different from those of which I spoke just now, which form real culs-de-sac, and do not pierce through the chorion.
Hence the internal face of the dermoid chorion exhibits three very distinct modifications. The first and last are seen to a small extent, whilst the second is almost general, with some differences however in the trunk, the extremities and the head. Besides, these modifications do not suppose a diversity of nature, but only of forms. Much separated and arranged in fibres in the first, the dermoid texture is compact and condensed a little in the second, and by this condensation renders the spaces less distinct. But there is a means of seeing them everywhere very well, where there is the least trace of them, and this is by maceration. This means also shows the dermoid texture best. In fact, when the skin has remained for some time in water, it softens, the fibres of its chorion separate, and their interstices become more distinct; then we see that the spaces exist not only on the internal surface, but that they extend into its texture which appears to be truly like a sieve in its whole thickness, so numerous are the spaces arising from the interlacing of the fibres.
These spaces do not terminate in culs-de-sac towards the external surface; they open upon this surface by many foramina which are very evident in a skin that has been macerated for a month or two, and which, in the ordinary state are almost imperceptible in some subjects, and very visible in others. Besides, in order to see them it is necessary to remove the epidermis; now as with the view of producing this effect immediately we commonly employ the action of boiling water or fire, the dermoid texture by this means acquires the horny hardening, and they become much less apparent, whereas maceration not only does not produce horny hardening of the skin, but it expands and dilates it, which renders these foramina very evident. In some parts of the skin and in certain subjects, we might then introduce the head of a pin into them; in others they are less evident. These foramina never pierce the dermis perpendicularly, all open obliquely to its surface; so that a perpendicular pressure tends to close them and bring their parietes in contact. I cannot compare their termination better than to that of the ureters in the bladder; hence why the hairs which go through them are never perpendicular, but oblique to the skin. We speak incorrectly when we say that the hairs are planted obliquely; their insertion in the bulb is perpendicular; it is in their passage through the chorion that they change direction.
Besides, these foramina are not vessels, but mere communications from the interior to the exterior through which pass the hairs, the exhalants, the absorbents, the blood-vessels and the nerves which go to the surface of the dermis; thus the subjacent spaces are only cells in which are contained the vessels of the glands and of the cellular texture. The dermoid texture should then be considered as a real net-work, as a kind of cellular texture, the cells of which very evident within, become less so on the exterior surface, with which all communicate to transmit to it different organs. The chorion is then the outline, the frame, if I may so say, of the cutaneous organ. It serves to lodge in its spaces, all the other parts which enter into the structure of this organ, and contributes to give them the form they are to have, but is wholly foreign to them.
What is the nature of this texture, which enters especially into the composition of the cutaneous chorion? I know not; but I think it has much analogy with the texture of the fibrous system; the following considerations support this analogy. 1st. On the heel, where the dermoid texture has the fibrous form of the irregular ligaments, it would be almost impossible to distinguish it from it, so uniform is the external appearance; it has the same resistance and density; the same sensation is experienced when it is cut with the bistoury. 2d. The dermoid texture becomes yellow and transparent like the fibrous by stewing. 3d. It melts gradually like it into gelatine. 4th. Like it, except the tendons however, it strongly resists maceration. 5th. Sometimes these two textures are identified; for example, the annular ligaments of the wrist evidently send elongations to the neighbouring dermoid texture. 6th. This texture can serve, like the fibrous, for the insertion of muscles; we see it in the face, where many of the fibres of the orbicularis of the lips and the eyelids, and almost all those of the eyebrows, find real tendons in the fibres of the dermoid texture. There is the same arrangement in the cutaneous palmar muscles.
All these considerations evidently establish many relations between the dermoid and fibrous textures. Yet they are far from being the same. To be convinced of this it is sufficient to observe how much their mode of sensibility differs, and how different also are their diseases; it seems at first as if there was no analogy between them in this double relation. Yet the line of demarcation is by no means as great as it appears to be. In fact the acute sensibility of the skin is not seated precisely in this white texture, which is interwoven so as to leave between its meshes the spaces of which we have spoken, and which we see especially on the surface adhering to this organ. The experiment mentioned in the article on the mucous system, and in which I irritated the cutaneous organ from within outwards, evidently proves it. It is the surface on which the papillÆ are found that especially exhibits this vital property.
On the other hand morbid anatomy proves that the internal surface of the dermis, in which are especially found the texture and the spaces of which we have spoken, is entirely free from most cutaneous eruptions. This is no doubt true as it respects the small pox, the itch and many species of herpes; I have satisfied myself of it as to the vaccine vesicles, the miliary eruption, &c. &c. It is certain that in erysipelas, the external surface only of the chorion is coloured by the blood which enters the exhalants; thus the slightest pressure, causing the blood to flow back, produces a sudden whiteness which soon disappears by the return of the blood into the exhalants. It is this which forms the essential difference between simple erysipelas and phlegmon, in which not only the external face of the chorion, but its whole texture and the subjacent cellular one are inflamed. In measles and scarlatina, the redness is also very evidently superficial. These phenomena accord with those of injections; for if they succeed at all in children, the skin of the face and less frequently that of the other parts, becomes almost entirely black. Now this blackness is much more evident on the external than the internal surface of the skin, no doubt because more exhalants are found in the first than in the second, which the arterial trunks only traverse.
The preceding considerations evidently prove that the texture of the internal surface of the chorion, and even that of its interior, have a vital activity much less than that of the external surface; that this texture is disconnected with all the great phenomena which take place upon the skin, with those especially which relate to the sensations and the circulation; that it is in the papillÆ that the first are seated and in the reticular body the second; and that it is almost passive in nearly all the periods of activity of this double portion of the dermis. Its functions, like those of the fibrous texture, suppose it to be almost always in this passive state; they are only to defend the body and to protect it from the action of external bodies. It is this which forms our real covering; thus its properties are well adapted to this use. Its resistance is extreme. It requires very considerable weight to tear very narrow strips of chorion, when it is suspended from them; drawn in various directions, these strips are broken also with much difficulty.
Yet this resistance is much less than when tannin is combined with the chorion. We know that when thus prepared, this portion of the skin affords the strongest strings we have in the arts. I know but two textures in the animal economy, which unite to such an extent suppleness and resistance; these are this and the fibrous texture; and this is a new character which approximates them. We have seen that it requires a very considerable weight to break a tendon, a strip of aponeurosis, or a ligament taken from a dead body. The muscular, nervous, arterial, venous, cellular textures, &c. yield infinitely more easily. If the dermoid texture had less extensibility, it might advantageously supply the place of the tendons, the ligaments, &c. in the structure of the body.
Since the chorion is foreign to almost all the sensitive and morbid phenomena of the skin, let us inquire then in what part of the dermis these phenomena are seated. These parts exist very evidently on the external surface; now we find on this surface, 1st, what is called the reticular body; 2d, the papillÆ.
Of the Reticular Body.
Most authors have considered the reticular body as a kind of layer applied to the external face of the skin between the chorion and the epidermis, pierced with an infinite number of openings through which the papillÆ pass. I do not know how we can demonstrate this layer, which escapes according to the opinion of most of them, when the epidermis is detached. In order to see it I have employed a great many means, but no one has succeeded. 1st. Such is the adhesion of the epidermis to the skin, that in a sound state we can hardly separate them without injuring one or the other. Yet with the greatest precaution we see nothing mucous on the chorion when it is laid bare. 2d. A portion of skin cut longitudinally, especially from the foot where the epidermis is very thick, allows us to see very distinctly on the divided edge the boundaries of this and of the chorion; now nothing escapes from about the line which separates them. 3d. In ebullition in which the epidermis has been removed, nothing remains upon the internal surface, nor upon the chorion. 4th. Maceration and putrefaction, the latter especially, produce upon the chorion a kind of glutinous layer the instant the epidermis is removed. But this layer is entirely the product of decomposition. Nothing similar is met with in the ordinary state.
I believe, from all these considerations, that there is not a substance deposited by the vessels upon the surface of the chorion, extravasated, stagnant upon this surface, and representing there a layer in the sense in which Malpighi understood it. I believe that we ought to understand by the reticular body, a net-work of extremely fine vessels, whose trunks already very delicate, after having passed through the numerous pores with which the chorion is perforated, come and ramify upon its surface, and contain different kinds of fluids.
The existence of this vascular net-work is placed beyond a doubt by fine injections which change the colour of the skin entirely externally, without altering it much within. This is, as I have observed, the principal seat of the numerous eruptions most of which are really foreign to the cutaneous chorion.
We may then consider the reticular body as a general capillary system, surrounding the cutaneous organ, and forming with the papillÆ a layer between the chorion and the epidermis. This system contains in most men, only white fluids. In negroes, these fluids are black. They have an intermediate tinge in the tawny nations. We know how much the shades vary in the human race. Hence the colouring of the skin resembles nearly that of the hairs, which evidently depends upon the substance existing in their capillary tubes; it is analogous to that of the marks at birth, that are commonly called nÆvi materni, and in which we never see a layer of fluids extravasated between the epidermis and the chorion.
Moreover, I think we know but little as yet concerning this substance, which fills a part of the external capillary system. It does not circulate in it, but appears to remain there till another replaces it. When we examine the skin of a negro, we see a black teint, and that is all. In maceration I have observed that this teint is sometimes removed with the epidermis, and that it sometimes remains adhering to the chorion. It is very evidently foreign to both, since both have the same colour in whites as in blacks. It is never reproduced, after it has been removed; for cicatrices are white in all people.
Is there in white people a white substance which, remaining in the external capillary system, corresponds to that of negroes, or does the colour of their skin depend only upon the epidermis and chorion? I have been tempted to believe that they also have a colouring substance, since the long-continued action of a powerful sun evidently blackens them. This circumstance has even made me believe that whiteness is natural to all men, and that there was but one primitive race which has degenerated according to different climates.
But in order to be convinced of the diversity of races, it is sufficient to observe, 1st, that the teint of the skin is but one of the characters which distinguish each race, and that many others are always united to it. The nature and form of the hair, the thickness of the lips and the nose, the width of the forehead, the degree of inclination of the facial angle, the whole appearance of the face, &c. are constant attributes which indicate a general modification in the organization, and not merely a difference of the dermoid system. 2d. White people become tawny in hot countries; but they never acquire the teint of the people of the country. 3d. Removed to cold countries in early age, or even born in them, the blacks always remain so; their shade hardly changes at all from generation to generation. 4th. Colour by no means follows temperature exactly; we see many varieties in the shades of people who live under the same degree of latitude, &c.
Every thing proves then that the colour of the skin is but an insulated attribute of the different human races, though it is that which is most striking to our senses, and that we should not attach to it a greater importance than to many others which are drawn from the stature, which is oftentimes very small, as in the Laplanders, from the broad and flat face, as in the Chinese, from the dimensions of the chest, of the pelvis, the extremities, &c. It is from the differences of the whole, and not from those of an insulated part, that the lines of demarcation should be made which separate the races. The European face and forms are in general the type with which we compare the exterior of the other nations. The ugliness or beauty of the human races are, in our way of considering it, measured by the distance which separates these races from ours. Such is in fact the force of habit with us, that we rarely judge in an absolute manner, and that every object which is much removed from those to which we are accustomed, is disagreeable to us and sometimes even disgusting.
Besides, the colouring matter of the cutaneous reticular body is more interesting to the naturalist than to the physician. What should particularly arrest the attention of the latter is the portion of the capillary system exterior to the skin in which the fluids circulate. In fact, besides the portion which is the seat of colour, there is evidently another that the white fluids constantly pervade, in which they are moved with more or less rapidity, and in which they continually succeed each other. It is from this portion that the exhalant pores arise which furnish the sweat; it is this vascular net-work which is the seat of erysipelas and of all the cutaneous eruptions that are foreign to the chorion.
The blood does not penetrate it in an ordinary state, but a thousand causes can at every instant fill it with this fluid. Rub the skin briskly, and it reddens in a moment. If an irritant is applied to it, whether it acts mechanically like nettles, the appendices of which penetrate the epidermis, or exerts a chemical action, like the frictions with ammonia, or the action of fire when a portion of skin is held too near it, instantly the sensibility of this vascular net-work is raised; it invites into it the blood which it formerly repelled; every part of a surface reddens in proportion to the irritation. If passion acts powerfully upon the cheeks, immediately a sudden redness is evident in them. All rubefacients exhibit moreover a proof of the great tendency which the sensibility of the superficial capillary system of the dermis has to place itself, if it be ever so little excited, in relation with the blood which in the ordinary state is foreign to it.
Vesicatories depend upon the same principle. Their first effect is to fill with blood the cutaneous capillary system, where they are applied, to produce in it a sudden erysipelas, and then to occasion a copious serous exhalation under the raised epidermis. They effect in a few hours what most cases of erysipelas do in many days; for we know that most of them terminate by vesicles which are raised above the skin. In burning, carried sufficiently far to be more than a rubefacient, and yet not so as to produce the horny hardening, there is also a sudden increase of exhalation under the raised epidermis. In general the production of every cutaneous bladder is always preceded by an inflammation of the external surface of the skin. This phenomenon is not exclusively confined to this system. We have seen the serous, as soon as it is laid bare and irritated considerably, redden in a short time by the passage of the blood into its exhalants; which constitutes an inflammation to which often succeeds a copious exhalation of milky or other kind of serum. This exhalation does not remain upon the surface, and does not form vesicles there, because it has no epidermis; this is the only difference between these phenomena, which at first view do not appear to be the same in the serous and cutaneous systems.
It is not only the irritation of the cutaneous organ which makes the blood pass into the external capillary system. Whenever the heart is powerfully excited and it accelerates the course of this fluid, it always tends to go into it; this is what is evidently seen, 1st, after violent running; 2d, in the hot period of a paroxysm of fever.
Upon this subject I will make a remark which appears to me to be very important; it is that the capillary system of the face is, more than that of all the other parts of the skin, exposed to be thus penetrated with blood. 1st. This is evident in the two cases of which I have just spoken, and in which the action of the heart is increased. 2d. In the passions, the skin remains the same in the other parts, whilst that of the face suddenly becomes pale or red. 3d. We know that physicians frequently examine the state of the facial capillary system, which is almost always affected by the state of the internal viscera, and is full of blood or empty, according as it is sympathetically influenced. 4th. In various kinds of asphyxia, in those especially produced by submersion, by the vapour of charcoal, by strangulation, &c. the face is uniformly of a violet colour from the passage of the black blood into its external capillary system, into which it is brought by the arteries. Oftentimes the neck and the upper part of the chest are also livid; but there is never a discoloration of the inferior parts. 5th. In many diseases, in which death takes place by a kind of asphyxia, because the lungs are the first interrupted, the dead bodies have a violet-coloured and swollen face; this may be easily observed by all who frequent dissecting rooms. There are a hundred subjects in which the head has this lividity, to one in which it is observed in the inferior parts. 6th. Most cases of apoplexy produce the same lividity of the face.
To what is this extreme susceptibility of the facial capillary system to admit the blood owing? Three things, I think, principally contribute to it. 1st. The course is already opened to this fluid, since the redness of the cheeks necessarily supposes its presence in them, it only increases in quantity; whereas when another part of the dermoid surface becomes red, all the blood which enters it is almost accidental. 2d. The anatomical arrangement of the capillary system is more favourable to this passage there than elsewhere; for it appears that the communications of this system with the arteries of the chorion are more free. What proves this is, that in injections the face is coloured with great ease. There is undoubtedly no anatomist who has not been struck with this phenomenon, especially in children, in whom if the coarse injections of our dissecting rooms succeed at all, the face becomes wholly black, whilst the fluid penetrates but very little into the other parts of the cutaneous system. 3d. It appears that there is a greater sensibility in the face; in fact the same irritant brings blood there, which does not make it flow to any other place. For example, a blow equal to a box on the ear does not redden the skin of the arm, whilst it suddenly inflames the cheeks.
The blood disappears from the facial capillary system as it enters it; in an instant the passions will successively produce there the bright red of a paroxysm of fever, the whiteness of syncope and all the intermediate shades. It is even the extreme ease with which this fluid penetrates this system, that renders the face well adapted to serve as a kind of picture, which the passions paint by turns with a thousand shades, that are effaced, altered, modified and return again according to the state of the mind.
I would observe upon this subject that the passions have in the face three means of expression; 1st, the capillary system, a means wholly involuntary, and which often betrays what we wish to conceal; 2d, the muscular motion, which, by contracting or expanding the features, expresses the melancholy or gay emotions, and to which belongs as effects, the various wrinkles of which we have spoken; 3d, the state of the eye, an organ, which, as Buffon has remarked, not only receives the sensations, but also expresses the passions. The two last means are to a certain extent voluntary; we can at least disguise them; whereas we cannot deceive by the first. The actor imitates anger, joy, &c. because we can give these passions by contracting the eye-brows, by dilating the face in laughing, &c. But it is the rouge of the actress that imitates modest chastity; it is by removing this rouge that she imitates the paleness of fear, horror, &c.
I will add another essential observation in respect to the facial capillary system; it is that it appears that its tendency to receive blood, disposes it to become the more frequent seat of many affections. We know, 1st, that erysipelas is much more frequent in this than in other parts; 2d, that the variolous pustules are remarkably conspicuous here; 3d, that many eruptions are more abundant here than elsewhere.
From all that we have just said, it is evident that it is necessary to distinguish two portions in the capillary system exterior to the chorion. 1st. One is constantly filled with the colouring substance of the skin, a substance which appears to be stagnant like that of the hair of the head, and that of the hair of the body, which is subjected only to the slow and insensible motion of composition and decomposition and which never exhibits that sudden increase or diminution of which we have just spoken. 2d. The second is constantly pervaded by many fluids which continually succeed each other there, and which constantly escape by transpiration, and which are replaced by the blood, that insinuates itself into this portion of the capillary system. These two portions are entirely independent, and have probably no kind of communication.
It appears that at the instant of death there remains a certain quantity of the white fluids in the second portion of the exterior capillary system; the following experiment, which I have frequently made, proves it; by plunging a portion of skin into boiling water, and leaving it there an instant, the epidermis is raised up, not as a whole as in a blister, but in an infinite number of small vesicles which are formed suddenly on its surface, and which contain a serous fluid, that escapes as soon as we open these vesicles.
PapillÆ.
We call by this name those small eminences that arise from the external surface of the chorion, and which, piercing the capillary net-work of which we have just spoken, become by their extremities contiguous to the epidermis. These eminences are very evident in the palm of the hand and the sole of the foot, where they are regularly arranged, in the form of small curved striÆ in different directions. We see them through the epidermis, notwithstanding its thickness in these places. But they are seen especially when this has been in any way removed, as by maceration, ebullition, &c. If we cut longitudinally a portion of the chorion of the foot, with its epidermis adhering to it, we see between them along the divided edge, a line in the form of a curved thread, which arises from these small eminences placed at the side of each other.
In some other parts of the skin, we distinguish the papillÆ in a very evident manner; but in a great number, the epidermis being removed, we see only a surface, slightly uneven from some small eminences, especially towards the orifices through which the hairs and the vessels pass, but we do not discover those regularly arranged eminences, the papillÆ properly so called.
We must not mistake for them the numerous and very evident prominences, which render the skin of some subjects extremely rough. These prominences are formed by small cellular, vascular or nervous bunches, by sebaceous glands, &c. which are found near the small openings by which the chorion opens under the epidermis, and usually transmits the hairs. These bunches, lodged in the small oblique canals which are terminated by these openings, raise the external side of them and thus form this prominence. The following very curious experiment proves this arrangement; when the skin is macerated for two or three months, or even less, on the one hand these little bunches in which there is almost always a little fat, are changed into that white, thick, unctuous matter, analogous to spermaceti, into which fat kept a long time in water is always converted; and on the other, the foramina enlarging, as we have seen, and the skin changing into a kind of pulp, we can easily remove it all around these little prominences, and see that they are continued with the fat which fills the meshes of the subjacent chorion, and which is also changed into a hard matter.
Injections have evidently proved to me that there were vessels in these cellular bunches, and I have been convinced of it for some time past by the dissection of some subjects that died of scurvy, in whom the spots commenced by very small ecchymoses, similar as it were to flea-bites, and which occupied these little eminences. The petechiÆ of adynamic fevers have a different appearance; but they belong also to an extravasation of blood in the cellular texture, occupying the small pores which open on the exterior of the chorion to transmit the vessels, the hairs, &c. The more prominent these eminences are, of which we have spoken, the more uneven is the skin. In general they are more frequent on the extremities and on the back, than on the anterior part of the trunk. In the extremities there are more of them in the direction of extension, than in that of flexion.
We attach the idea of a beautiful skin, to that in which these small tubercles are not found, and in which the chorion is united at its external surface. Women have commonly this last arrangement more evident than men. The epidermis which covers these eminences very often scales off at that place, especially from strong friction, which contributes still more to render the skin uneven, rough and harsh to the touch where they exist, which might induce a belief that they are formed by it, though it is always only accessory to them. Where it is very thick, as in the palm of the hand and the sole of the foot, it cannot be raised, and these small cutaneous tubercles are never seen. In the face where many vessels pass from within outwards, by the little pores of which we have spoken, we meet with hardly any more of them. The papillÆ scattered among these eminences, are in general very slightly apparent in the places where they exist.
All anatomists attribute to these last a nervous structure; they regard them as the termination of all the nerves that go to the skin, and which, according to them, are expanded to form these, after having first left their external covering. Some even say that they have traced filaments even into the papillÆ; I confess that I have never been able to do it. In the ordinary state, the density of the chorion and the extreme delicacy of the filaments, are evidently an obstacle to it. In the state of long continued maceration, in which the chorion becomes pulpy and in which we might consequently trace these filaments, were it ever possible, it cannot be done. I do not however deny the texture attributed to the papillÆ. The acute sensibility of the skin seems even to suppose it; but it is only analogy and not demonstration, which establishes this anatomical fact; indeed all the other senses, whose organs are so sensible, have the portion of them which receives the impression of bodies continuous with a nerve.
Action of different bodies upon the Dermoid Texture.
In most of the other textures, we have only considered this action in the dead body, because during life, these textures always removed from external bodies, cannot be influenced by them. Here we can regard it in a double relation, since the skin is incessantly in contact with almost all the bodies of nature.
Action of Light.
Light evidently acts upon the dermis. Removed from its influence, men are blanched, if we may so say, like plants. Compare the inhabitant of a city, who is never exposed to the influence of the sun, with the peasant who constantly is, and you will see the difference. It appears that it is the light and not the heat which produces the effect of which I have already spoken; for individuals who live in a warm temperature, but removed from the solar light, become white like those of cold countries. Thus we know that some men who keep their chambers always very hot, are whiter than others who, living in a less hot atmosphere, are constantly exposed to the sun. We might remain forever in a bath of a temperature equal to the warmest seasons, and the skin would not blacken. Apartments for study which are warmed with stoves, and in which men remain as long as the labourer at his plough, are as warm as the atmosphere of summer, and yet the skin of those who occupy them never becomes darker. Besides an irresistible proof is that the clothing which does not prevent the action of caloric upon the skin, and which offers a barrier to the rays of light only, prevents the cutaneous colouring that takes place upon the parts which the light immediately strikes, as upon the hands, the face, &c.
I do not speak of the solar influence upon the vital forces of the skin, as in cases in which sun-strokes produce erysipelas, or as when light is employed medicinally to recall the life of a part; but it is only in relation to the dermoid texture that I consider its action.
Action of Caloric.
The action of caloric upon the skin exhibits very different phenomena, according to the degree of it that it is applied.
1st. A warm atmosphere expands the dermoid texture, increases its action, and makes most of the fluids which form the residue of nutrition and digestion, pass off by the exhalants.
2d. When contracted by cold, this texture refuses to admit those fluids, which then go off principally by the urine.
3d. The insensible change from one to the other of these two states, does not disturb the functions. When this change is sudden, there are almost always alterations in different organs, because the fluids destined to pass out, cannot vary their direction as rapidly towards this or that organ, as the cutaneous excitement produced by the sudden changes from heat to cold.
4th. The skin resists a temperature much greater than that of the body; it opposes an insurmountable barrier to the external caloric, which tends to an equilibrium in animate as well as inanimate bodies. Thus whilst these last are penetrated with this fluid in a medium warmer than themselves, and soon acquire the temperature of this medium, living bodies remain at the same degree, how much greater soever the surrounding heat may be to their own. The curious experiments of the English physicians have placed this truth, as it respects man, beyond a doubt. It is unnecessary to give the detail of these well known experiments, in which the mercury was seen to descend in the thermometer, when the bulb was placed in the mouth and in which the skin became covered, in a heated room, with the aqueous vapours of the air, which the greater cold of the body condensed upon its surface. A slight attention to animals with cold blood, living in warm climates, proves the same thing. I will make one remarkable observation upon this point, it is, that most reptiles, whose temperature is much less than that of the mammalia and of birds, and who consequently are brought much nearer than them to the temperature of winter, cannot however support it. They become torpid and sleep in subterraneous places, the heat of which remains nearly uniform like that of cellars, and do not awake till the milder temperature of spring stimulates them.
5th. The skin, in very cold climates, seems to be on the other hand an obstacle which prevents the internal caloric from suddenly escaping and thus placing the body in equilibrium with the surrounding medium. This is evident in countries near the pole. Upon this subject an observation the reverse of the preceding can be made; it is that the cetaceous animals inhabit seas the temperature of which is most unlike their own. Whales are sought for especially in the latitudes of Greenland, Spitzbergen, &c. Why do fishes with warm blood delight in the frozen seas, whilst the amphibious animals with cold blood prefer the burning heat of the sun? I know not.
Let us observe that most of the internal organs when exposed in solutions of continuity, have not the faculty of preserving as well as the skin, a degree of independent temperature. They become cold or hot sooner than it as long as they remain healthy. The intestine brought out of the abdomen in the operation for hernia, a muscle laid bare, &c. &c. exhibit this phenomenon; thus in order to give them this faculty of having an independent temperature, nature inflames them, and they thus constantly preserve their heat, whatever may be that of the surrounding medium. The mucous surfaces next to the skin resist the surrounding temperature the most, as is seen in prolapsus of the rectum, in inversion of the anus, &c. This difference among the different systems is probably owing to that of their structure.
6th. When the action of caloric is carried to a very considerable extent, it begins to act upon the skin, and its effects are the more evident in proportion as it is the more intense. 1st. The slightest of these effects is to produce an evident redness, a kind of erysipelas; the caloric then acts like a simple rubefacient. 2d. The second is to redden the skin and then to produce vesicles on it. 3d. In the third there is a real horny hardening, a crisping of the fibres of the chorion which contract, like those of all the animal textures exposed to too strong a degree of heat. 4th. In the fourth and last effect, the dermoid texture is burnt, blackened and reduced to mere carbon. These different degrees of burning arise only from different degrees of caloric. I would observe that in the two first effects, this fluid acts upon the vital forces, and that these two effects cannot consequently take place except during life. The two last are exerted only upon the texture of the organ; thus they take place after death precisely as before. Cooks often employ the horny hardness, to give to the skin a hardness and brittleness necessary in some kinds of cooking.
7th. Cold carried to a great degree acts also upon the cutaneous organ, and produces different effects, according to its intensity. The first of these effects is very analogous to the first effect of a slight degree of caloric. It consists of a kind of local inflammation. The tip of the nose, the ears and the fingers, the cheeks, &c. become red from a slight degree of cold. I have not accurately observed the other effects between this and the last, which consists in a sudden privation of life. But there is this difference between the gangrene that then takes place, and that produced by a high degree of caloric, that the blackness is sudden in this last, whereas it takes place only as a consequence in the other. Observe in fact that there is in gangrene two things which physicians do not sufficiently distinguish, 1st, the mortification of the part; 2d, its putrefaction. The mortification is always antecedent; it is produced by a thousand different causes; sometimes by the ligature of an artery, as in aneurism; sometimes by that of a nerve; often by violent inflammation; sometimes by a contusion, attrition, a bruise, &c. Whenever a part is dead in the midst of those which live, whatever may be the cause of its death, it becomes putrid precisely like a dead body, every part of which life has left. Putrefaction takes place then even sooner, because on the one hand the natural heat of the body, and on the other the moisture of the surrounding parts, favour it remarkably. This putrefaction varies according to the state in which the part was at the instant of death. If much blood infiltrated it, as when inflammation destroys life, it quickly becomes putrid, blackens immediately and allows a fetid sanies to escape; this putrefaction is called moist. If there is but little blood in the part at the instant of death, its putrefaction is less sudden; it first putrifies, then blackens, and allows but little sanies to escape; this is the dry gangrene. Thus in a dead body, if one part is much loaded with blood, as the head of those that have died of apoplexy, its putrefaction is much more rapid and moist than that of the parts in which this fluid is less abundant. In the gangrene which succeeds mortification produced by cold, there is often dryness of the part, because there was but little blood in it at death. How little many physicians know of the progress of nature in the employment of antiseptics, which they apply in the living economy, as upon flesh without life. Antiseptics are applied for one of two purposes, either to prevent the death of the part, or its putrefaction. 1st. If it is with the first intention, antiseptics should be varied. By untying the artery of a limb of an animal that has been tied, you will perform an antiseptic operation. Bleeding and emollient applications which lessen the violence of inflammation in a phlegmon, are antiseptics. A tonic as wine and all stimulants which excite the vital forces in a part in which they are languid after a bruise, are antiseptics. This word is then extremely improper when it is applied to medicines designed to prevent the mortification of the parts. Antiseptics are employed to prevent a dead part in the midst of living ones becoming putrid; some effect is obtained; thus by sprinkling cinchona, muriate of soda, or any neutral salt, by moistening a limb, a portion of skin, the extremity of the nose, &c. which is dead from any cause, the putrefaction will be arrested, as in a dead body upon which the same means are employed. But what will be the result of it? a little less fetor in the surrounding parts and less danger of their receiving the influence of the emanations of the dead part; but it is always necessary that this should come off; antiseptics will never bring it to life. Hence it is evident that these means should be considered in two points of view entirely different. The first prevent mortification, and vary remarkably though they are designed to effect the same object; thus our means of curing retention of urine are very variable, oftentimes opposite, according to the cause which tends to produce this retention. The others prevent putrefaction, without restoring the parts to life; now these are uniformly the same, whatever may have been the cause of the local death.
Action of the Air.
The air acts incessantly upon the cutaneous organ. In the ordinary state, it constantly removes from its surface the sweat that is exhaled from it. Fourcroy, who has paid particular attention to the solution of the transpired fluid by the surrounding air, appears to me to have allowed too much influence to this solution upon transpiration. In fact there are two very distinct things in this function; 1st, the action of the exhalants which throw out the fluid; 2d, the action of the air which dissolves and evaporates it. Now the first of these is wholly independent of the other. Whether the fluid is dissolved or not, more is still furnished by the exhalants. If the solution does not take place, the fluid accumulates upon the skin, which remains moist; but this moisture does not obstruct the exhalant pores and prevent new moisture from being added to it. A comparison will render this very evident. In the natural state, the serous fluids are constantly exhaled and absorbed; the absorbents perform for them the functions of the air which dissolves the sweat; now, though these vessels cease to act, as in dropsies, the exhalants continue their action; there arises only a serous collection, which, though applied to the orifices of the exhalants, does not prevent them from pouring out more serum. The bladder in vain contains urine which presses upon the opening of the ureters, these ducts do not pour less into it. Though the mucous juices become stagnant on their respective surfaces, new juices are however poured upon these surfaces. So though the skin remains moist from the want of solution of the transpiration, more transpiration is nevertheless exhaled. Solution is a physical phenomenon wholly foreign to the vital phenomenon of exhalation. We transpire in a bath as well as in the air; only the fluid which arises from it is mixed with the water, instead of being reduced to vapour.
The moisture of the skin is owing to two causes wholly foreign to each other; 1st, to the increase of the fluid furnished by the cutaneous exhalants; now the action of these exhalants may be increased from three causes. First, every thing which accelerates the motion of the heart, as running, the paroxysm of acute fevers, &c. drives to the skin, as it is commonly expressed. In the second place, every thing which tends to relax and expand the cutaneous organ by a direct action exerted upon it by the surrounding bodies, increases also the action of these exhalants, as in the great heat of summer, as in a bath and after coming out, as in a heated room, &c. In the third place, the action of the skin is in many cases, sympathetically increased. Here may be classed the sweats of phthisis of which the lungs are the source; those of fear, which depend upon a sudden affection of an epigastric organ; those of many acute diseases, &c. Now in all these cases, however active the solution by the air may be, the skin will be constantly moist, because there is thrown out upon it more fluid than the air can dissolve. Thus in catarrhs of the lungs, in which more mucous juices are thrown into the bronchia than the air can remove, it is absolutely necessary that there should be cough and expectoration to carry off the remainder.
2d. There are cases in which the moisture of the skin arises from the solution not being sufficient. This is what takes place in the moisture of the bed in which the air is not changed, in damp weather, &c. There is not then more fluid exhaled; but the ordinary fluid becomes evident, because it is not dissolved. It is under this point of view that we must consider the action of the air upon the cutaneous organ which transpires. It carries off nothing in this organ; it has no real action upon it; it takes only what its vessels throw off. Solution is merely accessory, it is always subsequent to exhalation, and has no relation with it. In the same day, in which the temperature has remained the same, the skin is often dry, moist, humid and even wet with sweat. If the air acts upon transpiration, it is by contracting or relaxing the exhalants, and not by dissolving what they throw out. If the skin formed a sac without an opening, like the serous surfaces, transpiration would go on though it was removed from the contact of the air, the same as if in contact with it. Why in fact should not that take place there, which does upon these surfaces?
If we consider the action of the air upon the skin of the dead body, we see that it produces two different effects, according to the state of the body. If the air penetrates the skin on all sides, it dries it, and it then acquires a sort of transparency, like the fibrous organs, unless a large quantity of blood had been accumulated in it at the moment of death, in which case it becomes black or of a deep brown. Thus dried, 1st, it is firm and resisting, but can be bent in various directions without breaking, as is the case with many textures thus dried, as the cartilaginous, the muscular, &c. &c. 2d. It is much less easily altered than most of the other textures in a dried state. 3d. It absorbs moisture less easily than them, though however when immersed for a long time in water, it finally resumes nearly its original colour and loses its transparency. 4th. It does not exhale a very disagreeable odour, like many of the other textures. Hence why the skins of animals, merely dried, are used in many of the arts; why some barbarous people make use of them for clothing, &c. The aponeuroses, and the mucous, serous and fibrous membranes could not be thus employed. It is to this also that must be attributed the little alteration that takes place in the exterior of mummies, which would never last for ages, if clothed with a fleshy or serous covering.
When the skin is left upon the dead body, or exposed to a moist air, it becomes putrid instead of drying. Then it takes at first a dull colour, then a green and finally a black one. It exhales a very great fetor, swells and thickens, because the gases which are disengaged there fill the cellular texture in its little spaces. A mucous covering is spread upon its external surface, which is deprived of its epidermis. Nothing similar to this covering is seen on the internal surface. Finally, when all the fluids it contains are evaporated, there remains a black residuum, very different from that which is left after combustion.
Action of Water.
This action during life, is relative either to the substances that are deposited on the surface of the skin, or to the cutaneous texture itself.
The sweat deposits incessantly upon the epidermis many substances, the principal of which are taken away by the air, but many being slightly soluble in it, as the salts for example, remain on its surface, and adhere to it when not removed by friction. Mixed with the unctuous fluid which oozes out upon this surface, and with the different foreign particles that the air deposits there as everywhere else, these substances form upon the skin a deposit which cannot, like the transpiration, be carried off by solution. Now water removes all this deposit; hence why the use of baths is truly natural. All quadrupeds bathe themselves. All birds frequently plunge into the water; I do not speak of those for whom this fluid is as it were the element. It is a law imposed upon all species of animals whose skin throws out a considerable quantity of fluid. All the human races hitherto observed frequently plunge into brooks, rivers, or lakes, along which they take up their abode. The countries that are well watered are those which animals prefer. They avoid those where this fluid is wanting, or in which it is only sufficient for their drink. We oppose nature in every thing in society. In our own, numerous classes hardly ever use a bath; thus you must seek especially in these classes for cutaneous diseases. We have seen that the mucous juices, remaining too long upon their surfaces, irritate and stimulate them and cause there various affections. Is it astonishing that the residuum of the cutaneous exhalation which the air does not remove, should occasion various alterations upon the skin? In summer, baths are more necessary, because as many excretions are taking place by the skin, more substances are deposited there. In winter, in which every thing passes off by the urine, the cutaneous surface becomes less dirty, and has less need of being cleansed. After severe diseases, in which there has been copious cutaneous evacuations, one or two baths terminate the treatment advantageously. Let us consider water then as acting as accessory to the air upon the skin, as removing from its surface substances which the first cannot dissolve, substances, which varying remarkably like those that compose the urine, have presented the transpiratory fluids to chemists, sometimes as alkaline, sometimes as acid, oftentimes as containing salts, sometimes charged with odoriferous substances, &c. Water is the general vehicle; when it is evaporated, it leaves the substances that are not volatilized like it. It is on this account that dry frictions are also advantageous; they clean the exterior of the body.
As to the action of the bath upon the cutaneous texture, we know but little of it during life. They say in medicine that it softens, relaxes and unbends this texture; this is vague language to which no precise meaning is attached, and which is no doubt borrowed from the relaxation which the skin of dead bodies undergoes, or even tanned leather, when exposed to water. A bath acts upon the vital forces of the skin, raises or diminishes them, as I shall say; but it leaves its texture in the same state; it is only that of the epidermis which it alters, as we shall see.
Macerated in water of a moderate degree of temperature, in that of cellars for example which does not vary, the human skin softens, swells but little, becomes evidently whiter, and remains for a long time without experiencing any other alteration than that of a putrefaction infinitely less than that of the muscular, glandular, mucous textures, &c. subjected to the same experiment. This putrefaction, which removes the epidermis, appears to be much greater on the side nearest to this membrane; at the end of two or three months the skin loses but little of its consistence. It does not become pulpy as the tendons and muscles in this length of time when macerated; it does not become a fetid pulp till the end of three or four months. I have preserved some of it for eight months, which has still its primitive form, but which feels liquid under the fingers when pressed a little. In the half putrid state, the skin still preserves the faculty of crisping from the action of caloric; it moves about when placed on burning coals, or when plunged into boiling water. When once reduced to a really putrid state it loses this property.
Exposed to ebullition, the dermoid texture when well separated from the cellular, furnishes less scum than the muscular, the glandular and the mucous; it resembles in this respect the tendons, no doubt because being almost wholly gelatinous, it contains but little albumen. In the horny hardening that takes place a little before ebullition commences, it twists and then always becomes convex on the side of the epidermis, and concave on the opposite side; and for this reason; the fibres of the chorion in contracting by the horny hardening, are pressed against each other; all the spaces which exist between them are effaced; now, as these spaces are very large in the second direction, the dermoid texture necessarily becomes more contracted there, whilst in the first, the spaces hardly existing at all, every thing being almost solid, the fibres have less space to contract, they remain longer, and the surface continues larger. In the natural state the cavity of these spaces, being filled with cellular texture, increases the extent of the internal surface; this space then disappearing, this surface becomes contracted.
The moment this kind of twisting takes place upon the skin, it is covered, as I have said, with an infinite number of vesicles filled with serum, and which are formed by the epidermis. As this membrane is very thick on the soles of the feet, and the palms of the hands, it cannot contribute in those places to their formation, and we see nothing there similar to them. Yet by removing it from feet that have been boiled, I have observed that it contained between its layers many small vesicles, which were scarcely visible. I have not analyzed the water of these vesicles, but presume it is analogous to that of blisters. Besides a greater or less quantity of it is poured out, and the vesicles are consequently larger or smaller, according to the state of the external capillary system at the instant of death.
By the horny hardening, the skin becomes hard, elastic, very resisting, thicker, but not so broad. It soon loses its semi-transparency and yellowish colour, like the boiled fibrous organs. Then the hardness it had acquired at the instant of the horny hardening is gradually lost; it softens, gives out much gelatine in the water in which it is boiled, does not lessen in size, but even increases in thickness. Every kind of fibre, vacant space and organization is then gone; it is a membranous mass, homogeneous in appearance, semi-transparent and gelatinous. In this soft state, it does not lose the elasticity it had acquired in the horny hardening, like the mucous, serous, cellular textures, &c. &c. The great quantity of gelatine it contains still preserves this property in it. The least motion that is communicated to it produces a general trembling, a sort of vibration of all its parts, exactly analogous to that of the various kinds of animal jellies, half coagulated, which vacillate in the vessel from the least jar.
Finally, the ebullition still continuing, the gelatine is almost all dissolved, and there remains only a residuum like membrane and which disappears with great difficulty; it requires even a very long time for common boiling water to reduce the skin to this residuum. Such are the phenomena of the ebullition of the human skin as I have carefully observed them. Chemists have paid great attention to the dermoid texture of many other animals; they have formed different ideas of its nature; they have admitted that there are two substances in it; one fibrous and the other gelatinous. I refer to their works upon this point, particularly to the labours of Seguin, and the work of Fourcroy; for in general I do not relate what is detailed by others, it would be only a useless repetition.
Action of the Acids, the Alkalies and other Substances.
The sulphuric, nitric and muriatic acids act upon the skin, when in contact with it, as upon all the other animal substances. I have remarked however that their action is much slower, especially on the side of the epidermis, though this membrane may have been previously taken off. The first of these acids reduces it easily to a blackish pulp; the others bring it to a pulpy state with more difficulty, even when they are very little weakened; the oxy-muriatic acid produces hardly any effect upon it.
Some authors have said that the lapis infernalis produces the same phenomena on the dead as on the living body. I wrapped up in a piece of skin, as in a rag, many fragments of this substance, so that they were in contact with the epidermis; at the end of a day they were reduced to a kind of pap of a yellowish red, by the moisture which they had absorbed. The dermoid texture, crisped and contracted, had not been penetrated; it did not appear even to have been injured on the exterior. In general the action of the alkalies appears to be wholly different during life, and it varies even according to the different degrees of vitality. We know that flaccid and fungous flesh burns much less easily than that which is red and vigorous. It is the same with the acids. Never during life do they produce any thing analogous to that pulp of different colours according to the acids that are employed, which is always after death the result of their action.
We know that an alkaline solution, put in contact with the skin, produces a kind of unctuous and slippery feel, which is no doubt owing to the combination of the alkali with the oily deposit of the skin, from which arises a sort of soap.
I shall not speak of the tendency of the dermis to combine with tannin, nor of the phenomena of this combination; I should only be able to repeat what others have said upon this point. I will merely remark that it would be very important to try the effects of tannin on the large sub-cutaneous aponeuroses, the texture of which being essentially gelatinous has much analogy with that of the dermis, and which from their extent and delicacy might serve for uses to which the dermoid texture when tanned is less adapted. We know that the tanned skin is no longer what it was in the natural state, and that the substance with which it is then penetrated gives it an artificial consistence. If much tannin has been combined with it, it loses entirely the faculty of acquiring the horny hardness, and becomes brittle; whilst if but little of this substance is added to it, it preserves in part its suppleness and the property of crisping from the action of caloric. I would compare tanned skin to bone penetrated with the phosphate of lime, and that which is not tanned, to the cartilaginous parenchyma from which the acids have removed this phosphate.
II. Parts common to the Organization of the Dermoid System. Cellular Texture.
The whole dermis is penetrated with a large quantity of this texture. It is arranged in the following way; from the exterior of the sub-cutaneous cellular layer, an infinite number of elongations is detached which penetrate the contiguous spaces of the chorion, enter afterwards into those which are more exterior, and finally terminate in the numerous pores which transmit outwards the vessels, the nerves and the hairs, which have previously passed through this cellular texture. We can then consider the chorion as a kind of sponge, the spaces of which represent the interstices, and which the cellular texture penetrates on all sides; so that if it was possible to separate by dissection, these spaces from the cellular texture, and the organs which are in it, there would be a kind of sieve pierced in all directions. Art cannot arrive at it but with difficulty on account of the delicacy of the parts; but that which is not done by dissection, nature often effects. In biles I have observed that all that which fills the interstices of the dermoid fibres disappears by suppuration, and that these fibres, separated besides by the swelling of the parts, exhibit truly the appearance of a sieve of which I have just spoken, when the fluid that moistens them is removed. The bile differs in fact from many other cutaneous eruptions, in this that it attacks the cellular texture of the spaces of the chorion, whilst they have their seat, as I have said, in the reticular body. I do not know any acute affection which attacks the chorion itself; all have their seat either on its surface, or in the cellular texture of its cells. Its dense and compact texture seems, like that of the aponeuroses, not able to be changed until a length of time. In elephantiasis I have seen this texture evidently disorganized.
M. Thillaye showed me portions of skin taken from a cemetery, in which every thing that filled the dermoid spaces had disappeared, and in which these spaces and their dried fibres formed a real membranous sponge through which the light could everywhere be seen. In this case the reverse of what is seen in long continued macerations had taken place, in which the fatty cellular texture, changed into a solid, white substance, preserves, as I have said, the form of the spaces which it filled, whilst the dermoid fibres reduced to the pulpy state, are easily removed. In the first case it is the mould only which is left; in the second it is the substance which is contained in it.
In chronic leucophlegmasia, the sub-cutaneous serum gradually extends along the cellular elongations of the spaces of the dermis, separates their fibres, consequently enlarges these spaces, and sometimes penetrates even to the epidermis, which it breaks in different places, and through the crevices of which it escapes. In this case, there is not resolution of the skin into cellular texture, as it is called, but a separation of the dermoid fibres, which always remain.
I do not presume that the cellular texture of the chorion extends to its external surface, under the epidermis; for when this has been removed, fleshy granulations are not formed, now, in all the parts where the cellular texture is found, these granulations are produced, when the parts are laid bare.
Blood Vessels.
The arteries winding in the sub-cutaneous cellular texture, furnish an infinite number of small branches which are introduced with the cellular parcels into the most internal dermoid spaces, afterwards pass into those that are nearer, approximate by winding and anastomosing a thousand times through the spaces of the external surface of the chorion, finally go through the pores of this surface, and give rise to that external capillary net-work of which we have spoken in the article upon the reticular body, and to which in the ordinary state but very little red blood comes. In this course through the dermoid spaces, but few small arteries remain in the fibres of the chorion itself, as fine injections prove. These fibres resemble in this respect those of the aponeuroses through which many vessels pass, but which have but few belonging to their own texture.
The veins follow nearly the motion of the arteries, but in an inverse direction. After having passed through the dermoid spaces and the cellular texture which fills them, they go to the great sub-cutaneous trunks, which run a long course, form, as we have seen, a system wholly distinct by its position from that of the arteries and which can be often traced through the integuments. Not seen in the natural state, the venous ramifications of the spaces of the chorion are considerably dilated in the subjacent cancerous tumours, and make the skin which covers these tumours appear to be marked with blue lines, which always grow larger as the tumour increases. Whenever there is a considerable distention of the cutaneous organ by an aneurism, pregnancy, dropsy, &c. this dilatation also takes place, provided the cause of the distention pursues a chronic course; for nothing similar is seen in acute affections, whatever swellings may have taken place, as in those consequent upon fractures, upon compound luxations, &c.
All the black blood formed in the skin goes into the general venous system; no portion belongs to the abdominal.
Nerves.
Their distribution is nearly the same as that of the blood vessels. Many very considerable branches, as different divisions of the musculo-cutaneous, the internal cutaneous, the lumbar, the saphena, the anterior tibial, the intercostals, the cervicals, &c. form a kind of sub-cutaneous nervous system, from which go all the branches that enter the dermis. These branches, in passing through the dermoid spaces with the arteries and the veins, appear to anastomose often together, go through the pores which terminate the spaces on the interior, and no doubt form the papillÆ. Observe even that on the hand where the papillÆ are very evident, there are, in proportion to the surface, many more sub-cutaneous nerves than any where else.
Absorbents.
Many absorbents creep under the skin; it is here that they can be the most easily studied. All the veins are surrounded with them; various fasciculi are observed in their interstices; so that a layer of absorbents, arranged in the form of a continuous layer, seems to separate, in the extremities, the aponeurosis and the skin. There is no doubt that the origin of the most of these vessels exists in the chorion, that they carry to the blood the fat and the cellular lymph of its spaces, and the nutritive matter of its fibres. But is there a particular order of branches opening upon the surface of the epidermis to absorb in certain cases foreign substances? This question cannot be answered by anatomical inspection. But the following considerations appear to me to throw great light upon it.
1st. The sub-cutaneous absorbents, visible by injections, are too numerous in proportion for the mere purpose of carrying back the fat and serum of the neighbouring parts.
2d. There are many medicines which appear to be evidently absorbed; such are mercury in the venereal disease, various purgative and emetic substances, febrifuges even, as cinchona, which, when applied by friction, have produced their effects as well as if taken by the stomach; cantharides often act upon the kidneys, when the tincture is used as a liniment, narcotic substances sometimes occasion a weight in the head and drowsiness when they have been externally applied, &c. These different effects are well known and many authors have given examples of them.
3d. There is we know absorption of different kinds of virus, of that of hydrophobia, of the small-pox, of the venom of the viper, &c. an absorption, it is true, which rarely takes place when the epidermis is whole, but which uniformly does, when this being removed, the matter is found in contact with the external capillary net-work of which we have spoken. I would remark even that the different kinds of inoculation of the small-pox, of the vaccine disease, &c. evidently prove both the existence and importance of this net-work, to which heretofore sufficient attention has not been paid. There are many contagious principles which are absorbed through the epidermis; such are those of the plague which the clothes communicate and those of different pestilential fevers which penetrate by the skin more than by respiration. I believe cutaneous absorptions from which diseases arise may be divided in the following way:
| 1st. Absorptions which take place through the epidermis, and which produce an effect | { | 1st, local, as the itch, herpes, tinea capitis, &c. &c. |
| 2d, general, as pestilential diseases, putrid fevers taken in an unhealthy place, &c. &c. |
| 2d. Absorptions which take place only when the epidermis is removed, and from which arises an effect | { | 1st, local, as the vaccine disease, the small-pox, &c. &c. |
| 2d, general, as hydrophobia, the venom of the viper, a wound with an instrument impregnated with putrid matter, &c. &c. |
We see by this table that the absorbents when charged with injurious substances, sometimes do not transmit them beyond the part and sometimes carry them to the blood, which conveys them to the different organs of the economy. Some authors have thought that in those cases in which the effects of the absorption become general, there is rather nervous action and sympathetic phenomena, than the transmission of an injurious matter into the circulation, and that consequently the solids take almost an exclusive part in these diseases. But to remove all doubt upon this point it is sufficient to observe, 1st, that, in the absorption of many contagious substances, for example, when from the puncture of the finger with a scalpel impregnated with putrid substances, a pain is produced, there is even a redness along the whole course of the absorbents of the arm, and the axillary glands afterwards swell; 2d, that by transfusing into the veins most of the substances that are applied in frictions, effects analogous to those which take place in these frictions are produced. Thus purgatives and emetics, transfused or absorbed, act upon the intestines and stomach the same as if introduced in any other way. It seems to me that sufficient use has not been made of the experiments of the last age upon transfusions. By comparing their effect with that which takes place upon the cutaneous organ, I think that it is impossible not to admit a morbific principle in the blood, at the time of contagious diseases.
3d. After the use of mercury taken in frictions, the emanations of this metal from the animal fluids, act evidently upon silver when placed in the mouth, the rectum, &c. I am persuaded even that the blood which in the natural state exerts but very little action upon this metal, would alter it then. Accoucheurs know that the waters of the amnios of those women who have made use of mercurial frictions exhibit the same phenomenon.
4th. Many substances that are not medicinal can be transmitted to the blood by cutaneous absorption. Water appears to enter it in this way, in the rapid production of certain dropsies, in those cases related of travellers, who wanting fresh water on the ocean, have in part quenched their thirst by surrounding themselves with damp clothes, &c. When our garments are impregnated with the oil of turpentine, the urine soon acquires an odour that is owing to the principles transmitted to the blood by absorption. Many judicious philosophers have asserted that the weight of the body has been increased by a walk in the morning.
I have observed that after remaining in the dissecting room some time, the intestinal flatus frequently acquires an odour exactly similar to that which the bodies in putrefaction exhale. In the following way I convinced myself that it was the skin as much as the lungs that absorbed these odorous particles. I closed my nostrils, and fitted a long tunnel to my mouth, which passing out of the window allowed me to breathe the external air. The flatus from my bowels, after I had remained an hour in a small dissecting room, at the side of two very fetid bodies, acquired an odour nearly similar to theirs. I have observed also that by touching for a long time fetid substances, the flatus acquires more of this odour, than by remaining only in an air loaded with cadaverous exhalations. Then the absorbents carry at first these exhalations to the blood, which afterwards throws them out by the mucous surface of the intestines. Thus when the urine is absorbed, the saliva, the mucous juices, &c. have an urinous odour.
I could accumulate many other proofs of cutaneous absorption; but I have selected only the principal. Many others have been cited; Haller in particular, to whom I refer, has multiplied examples of it.
I would remark however that cutaneous absorptions have a character of remarkable irregularity; that under the same apparent influence, they sometimes take place and sometimes do not. It is thus that most often we absorb nothing in a bath, that we escape or take contagions, that the vaccine disease is or is not communicated, that the variolous inoculation is also often uncertain, &c. This is not astonishing. It requires a certain degree of sensibility in the skin for the absorption of this or that substance; above or below this degree, the absorbents repel this substance. Thus in the intestinal canal, if you raise by a purgative, the ordinary degree of sensibility of the lacteals, they cease immediately for a time to take up drinks, chyle, &c. and every thing passes off by the anus. Now a thousand causes act incessantly upon the skin; a thousand irritants by turns applied to it make the degree of its organic sensibility vary every instant, increase, diminish and remove it from that which is necessary for absorption. Is it astonishing then that this function should exhibit so many varieties? Many modern philosophers have produced numerous negative facts against cutaneous absorption. What do these facts prove? only the varieties of sensibility which I have noticed; but they do not destroy the mass of positive facts, generally acknowledged and which together form a body of proof which nothing can oppose. Thus we have seen the mucous surfaces variable in their vital forces on account of the variety of their excitants, vary also in their absorption. If in the serous membranes, in the cellular texture, in the work of nutrition for the organs, this function is uniform, it is because being constantly in contact with the same bodies, the surfaces where it is going on have an uniform degree of organic sensibility.
Many facts, in relation especially to contagions seem to prove that a state of weakness is favourable to cutaneous absorption. 1st. Children and women absorb more easily than strong and vigorous men. 2d. Many physicians have observed that in the night in which the cutaneous organ is in a state of remission in this respect, as it is not stimulated by external objects, contagious diseases are more easily taken. 3d. I have remarked that most of the pupils who have fallen sick during my dissections, had carried to their chambers portions of subjects, the emanations from which had been able to affect them during sleep. 4th. We know that practitioners recommend, that persons should not expose themselves to contagious miasmata during hunger, as the forces are then languid on account of the emptiness of the stomach.
Exhalants.
The external capillary system which surrounds the chorion and embraces the papillÆ, appears to be the origin of these vessels, as it is the termination of the arteries of the dermoid spaces. The exhalants take up their fluid there, which they throw out upon the epidermis. We have no anatomical knowledge as to their form, their length, their course and their direction; but their existence is incontestibly proved, 1st, by injections, which are sometimes poured out upon the whole cutaneous surface; 2d, by the sanguineous exhalation which takes place in some diseases in which there is a real bloody sweat; 3d, by the natural sweat and by transpiration, which can evidently have no other agents, though some authors have admitted that there were certain pretended glands for the secretion of these fluids.
An infinite number of calculations has been made to ascertain the quantity of fluid which the cutaneous exhalants usually pour out. We are dismayed when we read the result of the labours of many philosophers upon this point, when we go over the calculations, enormously multiplied, of Dodard, Sanctorius, Keil, Robinson, Roye, &c. To what do all these calculations, for which the life of a single man would perhaps be insufficient, tend? To prove to us that when we start from a false principle, the whole chain of consequences drawn from it is false, though these consequences may be rigorously deduced from each other. In fact, most philosophers have considered the skin as a kind of fountain with numerous capillary tubes, always throwing out in the same time the same quantity of fluids, and being able consequently to be subjected, like inert capillaries which pour out fluids, to proportions and calculations of quantity. But the results of these calculations have soon proved how mistaken their authors were. Read these results, and you will see that none of them agree, that frequently very great differences characterize them. Is this astonishing? A thousand causes make the transpiration vary at every instant. Temperament, exercise, rest, digestion, sleep, watchfulness, the passions, &c. increase or diminish the action of the cutaneous exhalants. I do not speak of the difference from climate, seasons, &c. which is still more decided.
An attempt has even been made recently to ascertain, what belongs to the urine, to the transpiration, to the pulmonary perspiration and to the excrements, to calculate the relation which exists between the quantities thrown out in these four ways; useless researches! We might obtain from them results for one man, which would not be applicable to others. Thus see if we have ever been able to make a single useful application to physiology or pathology of all these immense labours on transpiration. What would you say of a man who, during the days of the equinox, in which the state of the atmosphere was every minute changing, should try to establish proportions between the quantities of rain which fell in every quarter of an hour, or of one who endeavoured to fix relations between the quantities of fluids which are evaporated in given times, from the surface of a vessel under which the intensity of the heat which warmed the water varied every instant. The comparison is just. We might be able to say in general, at the end of a given time, nearly how many pounds of substances went from the body; and yet this varies in every individual. But to attempt to say in a general manner what, in this common quantity, the urine and transpiration separately furnish, is to prove that we do not understand the nature of the vital forces.
We have already observed, that all our knowledge upon the varieties of transpiration, is reduced to some general data; that, for example, in cold seasons and climates, it is by the internal emunctories that the residue of nutrition and digestion principally passes off, whilst in warm climates and seasons, it is the cutaneous organ that principally throws it out.
The skin on the one hand, and the kidneys and pulmonary surface on the other, are then in this respect, in a constantly inverse activity. Physicians very well know this difference in regard to the urine and sweat; they know that when one is increased, the other is diminished: that in winter the urine contains principles of various kinds, and that in summer the transpiration has a salt taste and other peculiar characters which it owes to the substances which are foreign to it in the first season. But they have not so well examined the relation of the transpiration with the sweat; this determined me to make the following experiments:
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 Foetus.
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 foetus 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 foetus, 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 foetus, 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 foetuses 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 foetus, 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 foetus 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 foetus? 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 foetus, 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 foetus 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 foetus is born, more or less coloured by it. Some foetuses 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 foetus 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 foetus, 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 foetus 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 foetus, 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.
