The adjective by which I characterize this system, is derived from the latin substantive which signifies the organs of which it is composed. Hair is found less generally upon man than upon most other animals. It forms upon them a kind of covering external to the skin, which, lessening in part the contact of external bodies, makes the cutaneous animal sensibility perform a less important part, and establishes less numerous relations between these bodies and them. External life is then, in this respect, more limited in them than in man, in whom a delicate epidermis and a few hairs thinly scattered over it, separate the organ of feeling from surrounding objects, the least impression of which is felt, and which, owing to this, keep the animal sensibility in permanent activity; thus man is designed to live more without than within himself. The pleasures of reproduction and digestion constitute exclusively the happiness of animals. That of man is in part the result of them; but an order of pleasures wholly different, purely intellectual and in relation only with external sensations, enlarges immensely by its presence, and contracts by its absence, the field of this happiness.
The hair of man covers especially the cranium, some parts of the face, the front of the trunk, the genital organs, the extremities, &c. The quantity varies remarkably, as well as the form, length, &c. In order to form an accurate idea of it, we shall now consider it separately in the different organs, we shall then treat of its general organization, properties and development.
ARTICLE FIRST.
EXAMINATION OF THE PILOUS SYSTEM IN THE DIFFERENT REGIONS.
This system must be considered on the head, the trunk and the extremities.
I. Pilous System of the Head.
The head is the part of the body in which this system predominates; it covers the whole cranium and defends it against the impression of external bodies, as the hairy coat of quadrupeds defends them. Thus this part is the least capable of exercising the sense of touch, either from the obscurity of the animal sensibility arising from this hairy covering, or because its convex form allows it to be in contact with external bodies only by a small surface.
The face is less generally covered with hairs, though many are found upon it, especially in men. This part, in which in a very small space are collected the greatest number of our means of communication with external objects, viz. the organs of taste, smell, sight and even hearing, has but very little to do with the sense of touch, on account of its villous arrangement. Its form is also badly adapted to this sense. The mouth which is flattened cannot be applied to external bodies. Thus whilst the snout which is elongated in most quadrupeds, performs the double function of first feeling all bodies, turning them in various directions in order to ascertain their tangible qualities, and then of seizing them for nourishment, the mouth of man serves only for this last use; it is the hands which are destined for the first. Thus observe that all animals, even the most of those with clavicles, almost uniformly direct their snout towards the earth, whilst the mouth of man is naturally destined to an opposite position.
Of the Hairs of the Head.
They occupy upon the cranium all the space which corresponds with the occipital, parietal, the squamous portion of the temporal and a small portion of the frontal bones. Their limits do not vary on the sides; they always correspond above the ear. Behind, they sometimes go down upon the superior part of the neck; at others, they do not extend beyond the head. In applying blisters on the ligamentum nuchÆ, we observe in this respect, almost as many varieties as there are subjects. We know how variable these limits are in front. Sometimes extended lower down, sometimes carried higher up, sometimes describing a curved line, and at others forming a real triangle the anterior point of which corresponds with the median line, they have really nothing constant.
These inequalities alone determine the breadth or narrowness of the forehead, whilst its degrees of inclination depend solely upon the bone which forms it. It is in this way that the hair contributes a little to the expression of the face; I say a little, for it is less to the breadth of the forehead than to its approximation to a perpendicular, that we attach the ideas of majesty and greatness which characterize heroes and gods. The poets, as we know, have particularly celebrated the forehead of the god of thunder. Observe in relation to this subject that there is a great difference between that which expresses majesty or abjectness in the face, from that which serves there to express the passions. It is the osseous structure of this region and the degree of inclination resulting from this structure, which serve for the first use, and it is especially the muscular motions which contribute to the second. Why? Because majesty, grandeur, &c. are especially connected with the extent of the understanding, and the understanding has its seat in the brain, and because the various capacities of the cranium, which contain this organ, and which correspond with its various degrees of development, have inevitably an influence upon the different dimensions of the face. Now as the bony structure is a thing constant and invariable, the air of majesty or abjectness remains always imprinted upon the face. On the contrary, the passions which especially affect the epigastric organs, which afterwards excite the facial muscles, have necessarily a transitory expression.
The number of hairs is very variable on the same surface. In some people they are very close together and even all touch; in others more thinly scattered, they allow in part the skin of the cranium to be seen in their interstices, a circumstance which is either owing to original conformation, or to a disease which makes them fall out in part. They have, like the nails, a determinate growth which they do not exceed. We know but little of the limit of this growth. Yet we have seen them reach to the waist, the thighs, and the legs even. It appears that in women they have a greater growth; we might say, that nature has compensated this sex in this way for the want of hair in many other parts. Floating upon the shoulders, the breast, the trunk, &c. they form in the natural state a sort of protection from the injuries of the air and the light. Their extent evidently proves that man was destined to an erect attitude. In fact, in the attitude of quadrupeds, they would trail much upon the earth, and form an obstacle to motion. The hair of no animal, I believe, in a natural attitude retards his progress so much, as the hair of man then would.
Man, who opposes nature in every thing, has made it a habit in most societies to cut the hair, the beard, &c. By common people, it is considered merely a thing of fashion; by the physician, as a practice which has perhaps a greater influence than is thought upon the functions. In fact, in the natural state when the pilous system has once acquired its growth, it no longer exhibits the constant motion of composition and decomposition. On the contrary, in man who cuts it, it is constantly the seat of this motion and of that of growth. This practice perpetuates then the phenomena which take place in them in infancy, and consequently keeps up there a more active work, which perhaps is performed at the expense of that of many other parts.
The natural difference of the hair has much influence upon its length; that which is smooth and curls but little is in general the longest. The more it has the opposite characters, the shorter it is, as is proved by that of negroes and those white people whose hair curls like theirs.
The tenuity of the hair is very great, yet its resistance is in proportion very considerable. There is no part in the economy, not even those of the fibrous system, which can support so great a weight in proportion to its size. Thus woven strings of hair would have an enormous resistance, if they were sufficiently long to be employed for different uses.
The colour of the hair varies remarkably according to country, latitude, climate, temperature, &c. This colour is even, like that of the skin, a characteristic attribute of the different human races. Naturalists have been much occupied with this subject, and I refer to their works.
In our climate the principal colours are black, flaxen and bright red. They are, as it were, the three general types to which may be referred many particular shades. The black has under it the brown, the chesnut, &c. The flaxen is connected on the one hand with the bright red and on the other with the chesnut. The bright red which touches the flaxen by one of its extreme shades, goes by an opposite shade to the natural colour of certain flames.
All physicians have considered the colour of the hair as among the characters of the temperaments. Black indicates strength and vigour. The figure of a wrestler with flaxen hair would be almost ridiculous. This colour is the attribute of weakness and delicacy; it floats upon the head of figures which painters have made strangers to the great passions, to powerful and heroic deeds; it is found upon the figures of young people, in pictures where laughter, sport, grace and pleasure preside over the subjects. These two colours, black and flaxen, as well as their secondary shades, are found distributed among women in nearly equal proportion; now reflect upon the kind of sentiment this sex inspires according to the colour of the hair, without regard to any other consideration, and you will see that a woman with flaxen hair creates a sentiment which beauty and weakness united seem to dictate. The epithets that we employ express this double attribute. On the contrary, the term brunette announces in her that it designates, a mixture of force and beauty. Beauty is then a common gift which attracts us, but which, differently modified by external forms, attracts us by touching, interesting and exciting us. Eyes in which langour is depicted, are frequently associated with flaxen hair; whilst black hair is almost always met with, in those whose vivacity and sparkling seem to proclaim an excess of life which seeks to be diffused.
Habit which accustoms us to every thing, changes our taste in regard to the colour of the hair, as it does to that of our dress. Black, flaxen and their numerous shades are in turns fashionable in France; and as the organization does not change with our taste, we have contrived artificial hair; a happy means, which seems to subject to our inconstancy the invariable course of nature, and which, changing at our will the expression which the physiognomy borrows from the hair, can at every instant exhibit man under forms which fashion extols to day, and which ridicule pursues tomorrow. Now among these numberless variations which succeed each other among us in the fashion of the hair, bright red and its various shades never find a place. Most people have a decided aversion to it. It is almost, in our eyes, a mal-formation to be born with it. This opinion is too general not to have some real foundation. The principle appears to me to be the usual connexion between the hair and the temperament and of course the character which results from this; now the kind of character connected with this kind of hair is not commonly the happiest, though there are many exceptions to this principle, which is proverbial. Another reason for the aversion to hair of a bright red, is that the oily fluid which lubricates it often exhales a fetid odour foreign to the other kinds of hair.
What is the relation that can exist between the hair and the character? Has the first an influence upon the second? No; the following is the way in which it should be considered. Every man has his peculiar kind of organization and constitution. This forms the temperament; now, to each kind is attached on the one hand this or that species of hair, and on the other the predominance of some internal viscera, which though less apparent is not less real. This predominance disposes evidently to certain passions, which are the principal attributes of character; then the colour of the hair and character are two different results from the same cause, viz. constitution; but one has no influence upon the other.
The hair coming out of the cutaneous pores has such a direction, that that of the anterior part of the cranium is almost always oblique in front, and tends to fall over the forehead; that of the middle and posterior part pierces the skin perpendicularly, and that of the posterior and inferior part traverses it obliquely, so as to fall naturally down the length of the posterior part of the neck. It is the same with that of the sides, which its direction as well as its weight, carries upon the region of the ear which it covers.
Eyebrows.
Upon the arch which borders the orbit above, is found a collection of hairs forming a portion of a circle more or less evident, which shades the eye and defends it from the too powerful impression of the rays of light. The hairs of the eyebrows are thicker together in persons of dark complexion, than in those of light. More numerous within, they sometimes unite together the two eyebrows upon the nasal prominence, and thus shade the root of the nose. Fewer without, they there cause the eyebrow to terminate in a point. All are obliquely directed from within outwards. Sometimes towards the internal side, they go perpendicularly forwards. Their length is scarcely more than half an inch; they do not exceed this except in some extraordinary cases. Their colour is usually, though not invariably, the same as that of the hair. They are firmer, more resisting and larger than the hairs of the head. If they were longer they would curl like the hairs on the genital parts, of the nature of which they partake.
The eyebrows enjoy two evident motions. 1st. They are depressed and carried inwards, by forming over the eye a very evident arch. 2d. They are raised up and separated from each other, by expanding the parts around the orbit. The length between the extremes of these two motions is nearly an inch. The first motion takes place to defend the eye from a very bright light. It expresses also the melancholy and gloomy passions; hence the reason no doubt why the same word is applied to the moral state of the mind, and to the row of hairs of which we are treating. Observe on this subject that the sanguineous and choleric temperaments, which are the most disposed to the passions which make the eyebrows contract, are precisely those in which the hairs that compose them are found in general the most evident. The second motion enables us to receive upon the region of the orbit a great quantity of the rays of light; it allows us to raise the upper eyelid to a great extent in order to open the eye wide, which the first evidently prevents. It expresses also the gay passions, those which dilate the face. Painters have studied more than anatomists, the different degrees of elevation and depression of the eyebrows.
Eyelashes.
Upon both eyelids there exists a small row of hairs, a little longer than those of the eyebrows, of the same nature as them, directed obliquely forwards, crossing each other when the two eyelids are brought together, and serving to defend the eye from the small particles floating in the air. In general they do not curl; when they do and turn towards the eye, an irritation ensues, and they must be cut off. Sometimes a bad direction is the cause of this irritation.
I would remark on the subject of the eyelashes, that all the openings of communication with the interior, as those of the meatus auditorius externus, the nose and the anus, and oftentimes also the orifices of the lactiferous tubes, are surrounded with a great number of hairs which defend these openings from external bodies. Around the mouth the beard takes the place of these hairs; the urethra has none, but the prepuce at its orifice is instead of them.
Beard.
The males of most animals are distinguished from the females by some external productions. The comb of the cock, the mane of the lion, the horns of the stag, &c. are examples of these distinctive characters. In man, the beard is the principal attribute of the male. It occupies all the chin, the sides of the face, both lips and the superior part of the neck. It leaves the cheeks bare as well as the parts around the eyes; thus observe that it is there that the passions are principally depicted, the expression of which would be concealed by the hairs, if the lower part of the face was the seat of them.
The beard, not so long in general as the hair of the head, is longer than that of every other part of the body. It is very commonly of the colour of the first, though more rarely flaxen and is more frequently of a bright red, which it often is in persons with flaxen hair. The nature of the hairs of the beard is the same as that of the hairs of the genital parts, the eyebrows, &c. They curl, are stiffer, more resisting and uniformly less oily than the hair of the head.
The quantity of beard varies remarkably in different men. Those in whom it is abundant and of a deep black are in general strong and vigorous. Observe also that the strongest males in the different species of animals are those, in whom the external production which distinguishes them from the females, is the most conspicuous. We might say that this characteristic production is the index of the strength or weakness of their constitution. A small lion has not a noble mane; great horns belong to a well made stag, and long, twisted ones to a good formed ram. Observe that it is not the same with the other hairs common to the two sexes. Often in a weak man, those of the arms, the thighs, &c. are as evident and even more numerous, than in the most muscular.
The habit of cutting the beard as most Europeans do, of preserving it like the Asiatics and of dressing it in different ways like the Chinese, gives a different expression to the face which characterizes the people. A masculine, vigorous physiogomy which expresses strength and energy, cannot be deprived of this external attribute without losing a part of its character. That of the Orientals exhibits an appearance which coincides with the strength of their bodies, and forms a contrast with the effeminacy of their manners. I do not know if, in consulting the history of the different people who allow their beard to grow, and that of nations who cut it, we might not be tempted to believe that muscular force is to a certain extent connected with its existence, and that this force is always diminished a little when we are constantly deprived of it. Every one knows the vigour of the ancients, that of the people with long beards, and that even of certain men who, among us, allow their beards to grow in conformity with the laws of monkish institutions. No doubt many causes may make weakness exist with a beard; but in a general view I think we can admit that there is a certain relation between it and strength. Take from a cock his comb, which is the characteristic of the male, as the beard is that of man, and he will lose strength. I am persuaded that we might take from the lion a part of his power by taking away his mane. We know the result of the experiments of Russel upon the castration of stags; their horns, after this operation have grown in an irregular manner, or have not even grown at all. This external attribute of the male in this species, appears as we know at the period of virility, when the vital forces are increased. It is the same with the human beard. This coincidence would alone prove that the use of this last is to serve for an external character to the male sex. The eunuch, whose powers are feeble, loses also oftentimes much of his beard.
Such are our prejudices in regard to the idea we form of beauty, that we ridicule what is really and absolutely so, for that is certainly so which indicates organic perfection. A peacock without his tail of emeralds, a ram or a stag without their horns, displease us; why does not man without his beard?
II. Of the Pilous System of the Trunk.
The hairs on the trunk are very variable. Some men appear as it were shaggy, whilst others are almost without hairs. There are more of them generally on the anterior than on the posterior part of the trunk. It is principally along the linea alba and upon the chest, that they are found in man. This last part is in general destitute of them in woman, who has usually very few on the trunk.
Both sexes have a very considerable quantity on the genital parts. They are there, as I have said, of the nature of the beard. Less frequently flaxen than the hair of the head, as frequently of a bright red, they are most usually black. They are, next to the beard, the longest hairs. They have generally no determinate direction; each hair almost has a different one. Few animals, like man, exhibit this excess of hair upon the genital parts. There is a great difference in individuals as to its quantity. The blackness and abundance coincide in general with strength.
III. Pilous System of the Extremities.
Man has many hairs upon the whole surface of his extremities. The proportion of number is nearly the same in all; but the length varies very much; in some, they form only a down; in others, they are a little longer; whilst in others, they are nearly of an inch in length, reach over each other, and give the extremities a shaggy appearance.
At the top of the superior extremities, there is in the hollow of the axilla a collection of hairs which are longer than the others, and are nearly of the nature of those of the genital parts. Nothing similar is seen on the inferior extremities.
The pilous system does not exist on the internal part of the arm and fore-arm in many men, in whom we see it only behind and on the sides. It is more uniform on the inferior extremities. The back of the foot and hand always have hairs. They are never seen on the sole of the one or the palm of the other; a circumstance of essential advantage to the perfection of touch.
ARTICLE SECOND.
ORGANIZATION OF THE PILOUS SYSTEM.
Whatever varieties exist in the form, size and arrangement of the hairs, their organization is nearly the same in all. We shall now examine this organization in a general manner. Chirac, Malpighi and all anatomists since them, have explained very well in some respects, and very badly in others, the structure of the hairs of the head, which is nearly the same as that of all the other hairs. The following is what careful dissection has shown me concerning it.
I. Origin of the Hairs.
The hairs of the head, and in general all the hairs, arise from a sub-cutaneous fat, or the cellular texture of the parts which are destitute of this fluid. Each is contained at its origin, in a kind of small membranous canal, the nature of which is perfectly unknown to me, and whose transparent parietes allow the hair to be plainly seen, when we have separated them with a delicate scalpel from the surrounding parts. This small cylindrical canal accompanies the hair to the corresponding pore of the skin, insinuates itself into this pore, passes through it, extends to the epidermis and is intermixed there with the texture of this membrane, but goes no further. The length of this canal, and consequently of the course which the hair runs under and in the skin, is nearly five lines in the hairs of the head. There is no adhesion between the hair and the internal surface of this small canal, except at the enlarged base of the first where, it receives its nourishment. Thus, by opening the canal at this place, and destroying its adhesions there, the hair becomes free, and is drawn from without inwards with great ease, by taking hold of its enlarged end with small forceps. In this way, the canal is insulated. I have thus dissected and separated, upon a surface of two inches, a very great number of these canals which appear, when nothing but them is left on the internal surface of the skin, like so many small elongations of it.
Are there vessels and nerves in this small cylindrical sac which contains the origin of the hairs? We see distinctly elongations going to its external surface, especially towards its extremity opposite to the skin; but dissection does not teach us the nature of these elongations. I have never been able to trace them to a neighbouring vessel or nerve. Haller has not been more successful, though he speaks of authors who have traced nerves to the origin of the hairs. I presume however that these elongations are especially vascular. Is there a fluid between the origin of the hair and its covering? By opening the latter, nothing escapes, though some authors have pretended the contrary. Besides, if this fluid is in the form of dew, as upon the serous surfaces, it cannot be distinguished.
It is in the middle of this small cylindrical sac, of which I have just spoken, that the origin of the hair is found. We see at its extremity an enlargement oftentimes almost insensible, at others very evident, though always less than has been said. This enlargement is of the same colour and nature as the hair itself. It adheres to the canal very probably by the vessels and perhaps the nerves it receives from it. The hair which arises from it goes through its canal without adhering, as I have said, to its parietes, passes with it through the oblique pore of the dermis, leaves it at the epidermis, and goes outward.
All authors say that the hair does not pierce the epidermis, but only raises it up, and that this forms a sheath which accompanies it to its extremity. This assertion is incorrect; in fact, 1st, the hair is as thick in its canal of origin as it is out of it. 2d. This canal being opened at its extremity opposite to the skin, we can draw out of it, as I have said, the whole hair with great ease, and without the least resistance; which would not be the case however if the covering of the epidermis was to be broken. It appears that from the enlargement of its extremity, the hair has no adhesion either in the sub-cutaneous canal, or in its passage through the skin, or the epidermis. 3d. If the cutaneous epidermis was raised up to cover the hair, this would have a treble thickness, unless this epidermis became wonderfully thin upon it. 4th. We do not see this pretended rising up by drawing out a hair of the head; on the contrary a depression exists at the place where this comes out. The cutaneous epidermis furnishes nothing then to the hairs, though the nature of them may be in part the same as its own, and it is proper to consider them as uniform in their structure from one extremity to the other.
Under the skin, through it and out of it, the hair is composed of two distinct parts. One external, forms a canal which extends from the enlargement of the dermoid extremity to the opposite one; the other internal, which composes as it were the medulla of it, is of an unknown nature.
II. External Covering of the Hairs.
The external covering of the hair appears to be of the nature of the epidermis. It has in fact almost all the attributes of it. 1st. The hairs of the head burn exactly like this membrane, give out when burning an analogous odour, and leave after combustion a similar kind of coal; now it is principally to the external portion that these phenomena are owing. 2d. Water penetrates the hairs with great ease; hence very useful hygrometers can be constructed with them; now the same is true of the epidermis; and moistened hairs in foggy weather present in this respect a phenomenon analogous to that of the epidermis softened, wrinkled and whitened by the contact of a cataplasm. 3d. It is by means of the epidermoid covering that the hairs are foreign to life, that they are insensible and never become the seat of any acute or chronic affection. 4th. This covering is white, whatever may be the colour of the hairs. The cause of the colour resides in the internal medulla; thus the epidermis of negroes and that of white people differ but very little. Hence why when the internal substance of the hair has disappeared, the canal remaining alone exhibits a more or less evident whiteness. 5th. In this state, though the interior of the hair may be dead, the epidermoid exterior, which is independent of it, preserves most commonly the faculty of growing when it is cut; thus the cutaneous epidermis is truly foreign to all the subjacent diseases of the skin. 6th. I presume that it is this covering which gives to the hairs of the head the property of remaining so long uninjured. When removed far from the access of the air, they remain unaltered for ages; they have not in them the principle of decomposition of the other animal substances. They never become putrid either in air or water. Thus we have seen that the cutaneous epidermis never undergoes putrefaction, which seizes upon the subjacent parts.
It appears however that the hairs are more unalterable than the epidermis, and that there is even a difference of nature between them. In fact, 1st, maceration and ebullition, which make the epidermis very easy to be broken, though they soften it but little, leave the hairs with their usual resistance, unless carried to degrees that I have not tried. By boiling and macerating them comparatively with the epidermis, we easily make this observation. 2d. The acids act less efficaciously upon the hairs than upon this membrane; but the alkalies dissolve them with as much and even more ease. 3d. A thread of epidermis of equal thickness would be incomparably less resisting than a hair. 4th. The hairs can, like the epidermis, be painted of different colours; but they do not retain them so long, and on this account the colour must be renewed oftener.
Some modern authors have said that there is detached from the external covering of the hairs a kind of scales which form as it were little branches to them. We do not see these elongations. However the experiment mentioned by Fourcroy, and which consists in this, that by rubbing a hair between the fingers, it is raised like the heads of some species of grain in the direction from its base to its point, this experiment, I say, appears to prove the existence of these insensible elongations, which perform also an essential part in the adhesion of the hairs of the head to each other, an adhesion that is such that when they have remained a long time without being separated, as in long diseases, it is only done with the greatest difficulty.
Sometimes the hairs are bifurcated in a very evident manner at their extremity.
It is the greater or less thickness of the epidermoid covering of the hairs, which constitutes the different nature of them. Thick and compact on the genital parts, the chin, &c. it is less easily penetrated with water, and renders the hairs more elastic there and more capable of curling. Loose and thin in the hairs of the head, it makes them more smooth, and gives them more sensibly the property of the hygrometer. It is the peculiar nature of this external covering, which gives to the hairs of the head and the hair of negroes the character which distinguishes them.
From what we have just said it is evident that the external covering of the hairs of the head is the part of them which is essentially inert and foreign to life. It is not the same with their internal substance.
III. Internal Substance of the Hairs.
This substance is the most important; it is this which essentially characterizes the hairs, which I should have ranked in the epidermoid system, if they had nothing but their external covering, as is the case when they become white.
We are entirely ignorant of the nature of this internal substance. It can only be presumed that there are extremely delicate vessels inclosed in the common epidermoid covering containing a colouring substance, which stagnates in these vessels, or at least is subjected in them to a very slow nutritive motion. Among these vessels, do any of them as on the skin, open outwards to throw off fluids? Many physiologists have thought so, and on this account they have considered the hairs as real emunctories. I do not believe that we have any anatomical data upon this point; but the plica polonica, a singular disease in which the hair when cut pours out blood, evidently proves that they have exhalants in a natural state, which then becoming enlarged and dilated, pour out a fluid that they before refused to admit. Besides, there is no doubt that the pilous exhalants, infinitely less active than the cutaneous, are a much less copious emunctory. As to the absorptions which some have pretended are made by the vessels of the hairs, I think that nothing can prove them.
From what we have just said upon the internal substance of the hairs, it appears that it has a true analogy with the reticular body of the skin, and that, like it, it arises from two sorts of vessels, one in which the colouring matter stagnates, the other which gives passage, in some cases at least, to fluids, and in which there is consequently a kind of circulation.
The colouring substance of the hairs has some analogy with that of the skin. Thus we observe that the first, like the second, is blacker in warm climates and nearer the equator than in colder ones; thus red hair is frequently found with freckles which are more or less abundantly spread upon the skin of some people, and which are evidently seated in the reticular body, as I have ascertained in many patients who had these marks, and in whom the epidermis was raised up either by erysipelas or a blister. The acids however change the colour of the hair more than they do that of the skin of negroes. The muriatic whitens at first the hairs of the head which become yellow in drying; the nitric yellows, and the sulphuric leaves them black.
That which especially interests us in the internal substance of the hairs, is the real vitality which it enjoys, and which essentially distinguishes it from the external covering. It is to this character that must be referred the following phenomena.
1st. The different passions of the mind have a remarkable influence upon the internal substance of the hairs. Often, in a very short time, grief has changed the colour of it, and whitened it by occasioning no doubt the reabsorption of the fluid contained in the small capillary vessels. Many authors have related facts of this kind. Some, even Haller, have doubted them. But I know at least five or six instances in which a discoloration has taken place in less than eight days. The hair of a person of my acquaintance became almost entirely white in the course of a night upon the receipt of melancholy intelligence. In these changes, the epidermoid covering remains the same, preserves its texture, its nature and its properties; the internal substance only is altered. It is said that terror can make the hair stand an end; painters express it even by this external attribute; I know not to what extent we should give belief to this phenomenon which I have never seen; but it is an opinion too generally received not to have some real foundation. Now if fear acts so powerfully upon the hair, if it can give it a real motion, is it astonishing that grief and pain should suddenly change the fluids that are found in it, and deprive it even of these fluids?
2d. The plica polonica, of which I spoke just now, in which the hairs of the head become, when they are cut or even when they are not, the seat of a bloody exhalation, and in which they have a remarkable excess of life, evidently resides in the internal substance; the epidermoid covering has no connexion with it. Some authors even say that this internal substance acquires sometimes a fleshy nature; then their covering is raised up in scales.
3d. We know the danger of cutting the hair after many acute diseases. I have already seen a melancholy instance of it. Many physicians, Lanoix in particular, have related others. Now, to what are these accidents owing? It is certainly not to the contact of the air, from which the hair defends the head; for these accidents take place, though the head may be covered. It can only be owing to this, that the growth of the hairs that are cut, calls to these organs a vital activity which the internal viscera soon sympathetically feel; hence the pains of the head, the affections of the eyes, &c. observed in these cases. It is a species of active sympathy exerted by the hair upon the viscera; now, every organ which sympathizes has a real vitality, and enjoys very distinct vital properties. The epidermis never takes part in sympathies, because it is almost completely inert, is hardly organized, is not at the level of the other organs, and cannot consequently correspond with them. The danger of cutting the hair after severe sickness, gives me opportunity to observe that it is often as dangerous to remove suddenly the vermin from the heads of children during these diseases. I have seen three or four instances of accidents from this cause.
4th. The hairs not only influence other systems, but are also influenced by them. This is what we often see after acute diseases, in which the roots sympathetically affected, repel the fluids that come to nourish them, die, and the hairs fall out. Observe that this falling out of the hair very rarely takes place at the same time with the desquamation of the epidermis; which proves, that the generally admitted opinion of the origin of the external covering of the hairs is entirely false, and that, though very analogous to the epidermis, this covering does not arise from it, as I have said.
5th. Many animals lose at one season of the year their hairy covering, which is afterwards reproduced; now the period of its regeneration is often that of many diseases, and almost always that of a greater weakness than at other times. We might say that the nutritive work which then calls to the exterior much vital force, diminishes this force in the other regions. Man is not subject to these annual renewals of the external productions which cover his body, like birds, many quadrupeds, reptiles, &c. It is a cause of less diseases. In fact, a thousand different causes would no doubt have frequently deranged these renewals in society, as a thousand causes disturb the menstrual evacuation, &c.; hence the various diseases we escape by the want of this renewal. Man is in general subjected to fewer causes of natural revolutions, than most animals.
6th. Heat and cold have also oftentimes an influence upon the internal substance of the hairs. We know that in some animals, as rabbits, hares, &c. they become white in the winter and resume their original colour in the summer.
7th. A short time after painting the hairs of the head black, a fashion now more common in France than at the period in which they powdered them, there is often experienced pains in the head and a swelling of the hairy scalp, though the skin has been in no way concerned, has not been pulled, and the hair only has been affected.
It follows from all we have just said, that the hairs analogous, by their external covering, to the epidermis; foreign by means of it, if we may so say, to life, belong to it much more particularly by their internal substance, a substance whose nature is yet but little known, as I have already said. What moreover evidently proves this assertion, is that the phenomena of which I have just spoken, and to which I could add many others, cease to be evident in persons, in whom the hairs having become white, have no longer any thing but the epidermoid covering, the internal substance having in part disappeared; particular observation proves this. It may be however that in this case that portion alone of this internal substance, corresponding to the colour, is destroyed, whilst that which is the seat of the exhalations continues to live as usual; and, in this respect, white hairs may experience vital phenomena, of which, I believe, there are a few examples. But all this is subordinate to the future experiments, which will elucidate the pilous structure more than it now is.
ARTICLE THIRD.
PROPERTIES OF THE PILOUS SYSTEM.
The hairs experience but a slight degree of the horny hardening when exposed to the action of caloric. They then turn in various directions, curl and twist; but this arises from a cause entirely different from that of the horny hardening of the other organs. The caloric then removes the moisture with which the hairs are constantly penetrated, and thus approximates their particles. Thus when the hair is moistened by fog, a bath, &c. the curls disappear. The oily substances that are used at the toilet, give a coat that is insoluble in water, and preserve the curling, by preventing it from penetrating the hairs. Some time after the head has been washed, they curl more, as we have had occasion to observe since the Grecian head dresses have been in fashion among us. This at first appears to be contradictory, but it is not so. In fact by then rubbing the hairs much, the unctuous substance is removed, which always surrounds them, or this substance combines with the soap, if the water contains it, as is often the case; by this means it easily penetrates the hairs, the pores of which remain open, and by afterwards evaporating with the fluids that were already there, and which the unctuous substance retained, it leaves these organs more dry than they were, and consequently more disposed to curl.
A proof, that it is the epidermoid covering which thus imbibes the moisture that it afterwards loses in the state which succeeds the curling, is, that the detached epidermis can be curled with a hot iron, and afterwards rendered supple by soaking it in water.
The contractility and extensibility of texture are very indistinct in the hairs; it is their resistance which prevents their rupture; they can hardly be stretched at all.
They have no animal sensibility when pulled; the pain that arises from it has its seat especially in the skin through which they pass. Thus when drawn opposite to their direction, we suffer much more than by stretching them in the direction of their pores. I do not deny however that these elongations, which fix their origin to the neighbouring parts, may be also the seat of pain when the hairs are pulled. These organs have no animal contractility.
The organic properties certainly exist in their internal substance. The changes which this substance undergoes can only depend on the different alterations which affect these properties. The organic sensibility and the insensible contractility especially are raised in it in a remarkable degree in the plica polonica; now in order to have the degree of energy which they then do, they must have existed there in a natural state. It is these two properties, that, the sympathies of which we have spoken, put into action. The organic contractility is nothing in the hairs.
Yet we cannot deny that in the natural state, these organs are, next to the epidermis and the nails, those in which life is the least active, those which have the least numerous relations with the other organs. Whilst every thing is destroyed in most of the other systems by diseases, this is most often unaffected by them; it grows as usual, and appears to be in no wise disturbed; it has then a manner of being, of existing, wholly different from the others.
In general, the external productions of animals, as the feathers, the hair, the scales, &c. seem to form a separate class of organs, foreign to the life of the internal organs; it is almost like the different species of mosses that grow upon trees, without making essentially a part of them.
ARTICLE FOURTH.
DEVELOPMENT OF THE PILOUS SYSTEM.
I. State of this System in the First Age.
In the first months of the foetus there are no hairs on the skin which is then gelatinous. It is when the fibres of the dermoid texture are formed, that there begins to appear on the head a light down, an indication of the hairs which are afterwards to arise. This down is whitish and concealed by that fatty and unctuous substance, which we have said is deposited on the external surface of the skin at this age. Soon this down, which appears to be but the external covering of the hairs, which is then of extreme tenuity, begins to be coloured black or flaxen, according to the tint that is afterwards to predominate; it is the internal substance that forms it. The colour remains faint until after birth. At this period the hairs are often more than half an inch long. Upon all the rest of the body there is only the down, the precursor of the hairs; the face especially has much of it. The hairs of the head are then in advance at one period of the other hairs, in their growth.
After birth the hairs grow much more rapidly than before. It is precisely the reverse of most of the other parts, whose growth is more rapid in the womb of the mother. During the whole of youth this system has a tint less deep, than it is afterwards to have. The flaxen becomes nearer the chesnut, and this nearer black, and the first tints of the bright red grow many degrees darker towards the period from the twenty-sixth to the thirtieth year. The light tints are to the pilous system in youth, what the imperfectly developed forms are to the muscular, cellular, &c. Oftentimes that which is to be afterwards flaxen, approaches a whitish tint, which is owing only to the nature of the internal substance, and not to its absence in old age. Thus the white of the Albinos depends also upon the peculiar species of this internal substance. Many hairs are wanting upon the body of the young man.
II. State of the Pilous System in the following Ages.
At puberty there is a remarkable revolution in this system which becomes almost double. The hairs of the genital parts are formed; the beard which is, as I have said, the characteristic attribute of the male in the human species, is also then developed. We might say that there was the same relation between the hairs of the neighbourhood of the testicles and those of the beard, as between the testicles themselves and the organs of the voice, between the womb and the mammÆ. The beard is, in this respect, the external sign of virility. Some time before it comes out, we see under the skin the sac which contains the origin of the hairs; it is already very evidently formed, and permits the principle of the organ to be seen which it is to contain, as I have oftentimes ascertained; thus the sac of the tooth exists a long time before the tooth is cut.
At the same time the hairs of the axilla grow also; those of the trunk and extremities, which were then almost in a state of down, become larger, assume a determinate colour, and increase even much in number.
Why does puberty occasion this general growth in the pilous system? This is asking the reason of all the other phenomena which appear at this period. I would only observe that the hairs of the head, the eyebrows, the eyelashes and the hairs at the openings of the body, are those which are the least affected by this revolution. Besides, this growth is gradual; it requires at least two or three years for the beard to become what it is always to be.
In the following ages the hairs undergo but few changes; they grow in proportion as they are cut in different parts, and are the seat of a constant external work; now, observe that this work is more prompt, and the growth of the hairs consequently more rapid, in summer in which the cutaneous organ is especially in action, than in winter in which it is contracted; an additional proof of the real vitality of the organic forces of the internal substance of the hairs.
III. State of the Pilous System in Old Age.
Towards the end of life, the pilous system is affected by the general obliteration which takes place in almost all the external vessels; it ceases at first to receive the colouring substance. The internal substance dies, the epidermoid covering remains alone; the hairs become white. The hairs of the head appear the first, and are the first to die. The beard, the hairs of the genital parts and then those of all the parts of the body afterwards die. Besides, there is a great variety among men as it respects the period in which the hairs whiten; in some, this phenomenon begins about the thirtieth year, and even sooner, in others it is towards the fortieth, fiftieth or sixtieth. A thousand causes arising from the passions of the mind, from diseases, aliments, &c. can have an influence in society upon this premature death, so common in many men, but which does not take place in animals, who are not exposed from their kind of life, to the same revolutions, until the last years.
The hairs, after remaining white for a longer or shorter time, finally fall out; then the sac which covered the origin of them flattens down and entirely disappears. I have examined many bald heads; the skin of the cranium was perfectly smooth on its internal surface, though it had been separated from the cellular texture. No trace is discoverable there of the innumerable appendices which the canals form, after the hairs they contain have been drawn inwards. I have also dissected a man who after a putrid fever had become almost entirely bald. There were all these little canals entire, and in the bottom of them could already be seen the rudiments of new hairs. There is then this difference between the falling out of the hairs of old people, and that which is the consequence of diseases, that every thing dies in the first, because the vessels which go to the root cease to transmit fluids to it; whereas in the second case the hair alone falls out, and its sac remains.
It is a pretty generally received opinion that the hair, the nails and the epidermis continue to grow after death. We have, I think, but few data respecting this singular phenomenon. I am however certain that I observed a real elongation of the hairs of a chin of a head that had been carefully shaved, and which I macerated eight days in a cellar. An attendant of the dissecting room, who prepares many heads for the bones, informed me that he had often made the same remark, when putrefaction is prevented for some time. What is certain also is, that the growth of the beard is not in the direct ratio of the vital forces; in the diseases which affect these forces with a general prostration, it grows as much as in those in which there is a general exaltation of these forces. We remark this in hospitals where at the side of an inflammatory fever, there is often found a putrid or slow nervous one. Besides, why should there not be sufficient tonic forces left in the hairs to grow some time after general death, as there is in the lymphatics to absorb, &c.?
The different phenomena which the hair, the epidermis, the skin, and in general all the external organs experience in the successive ages, are wholly owing, like those of the internal organs, to the laws of nutrition, and not to the action of surrounding bodies. This is an essential difference between organic and inorganic bodies. The latter are gradually altered in two ways by the contact of external bodies which act upon them, 1st, mechanically by friction, tearing, &c. &c.; 2d, chemically, by combining with them, as for example, the air whose different principles undergo many combinations which change its nature and that of the bodies with which it is in contact. In this respect all inorganic bodies grow old. At the end of some time, they have no longer the exterior which characterized them in the beginning. Observe monuments, pictures, engravings, earths, metals, stones, &c. &c. every thing which in the arts, commerce, sciences, in the uses of life or in the phenomena of nature is formed of any inert bodies, whether these bodies have never lived, or having lived, have not been able to preserve themselves after death, as the solid portions of vegetables, the bones, the horns, the hair of animals, &c. every thing finally has the indelible stamp of time; every thing grows old; every thing loses its freshness, every thing changes on the exterior of inert, as well as on that of organic bodies; but as in the first surrounding bodies alone have acted, the internal part is still young, whilst the external is old, if I may be allowed to use two very improper words. Thus the rock whose surface is blackened by the lapse of years, is the same in the interior as when it was created. On the contrary in animals and vegetables, the internal organs are worn out, as well as the exterior. Time is marked upon the viscera, as well as upon the forehead of the aged. Surrounding bodies act upon us, wear out life, if we may so say; but it is as stimuli that they exert their action; it is by exhausting the sensibility and contractility, and not by combination, mechanical contact or friction. Language ought to express this difference. We do not use the term young when viewing the exterior of a new building, a new garment, or a picture recently painted; why do we say an old monument, an old piece of cloth, &c.? if it is a metaphor, very well; but this word cannot express a state analogous in its nature, to that of an old animal, an old plant, &c.
IV. Preternatural Development.
There are three principal cases in which the hairs are preternaturally developed in the economy.
1st. Sometimes they are formed on the internal surface of the mucous membranes; they have been seen in the bladder, the stomach and the intestines; many authors have given cases of them. I have found them upon the calculi of the kidney. I have seen in the gall-bladder at one time a dozen of nearly an inch in length, and which were evidently implanted in its surface.
2d. There is often seen on the skin preternatural collections of them, which are usually a defect from birth. These collections are particularly observed upon some of those productions or irregular excrescences, that are called nÆvi materni. There was exhibited at Paris, six years since, an unfortunate person, who had from his birth his face covered with hairs almost like those of a wild boar; and to whom there came on at the age of thirty-six years, that particular species of elephantiasis, in which the skin of the face increased in size, exhibits, if we may so say, the features of the lion, a species which I have since had occasion to observe upon a natural skin. This double circumstance gave to the face of this man an air of ferocity which it is impossible to describe. Many of the stories circulated by the vulgar concerning men with the heads of wild boars, bears, &c. are nothing but these nÆvi in the face, with a growth of hair upon them.
3d. Hairs are often preternaturally developed in cysts, in those of the ovaria especially. A great many instances have been related. Haller in particular has collected many; I have seen two. The following is what they exhibit; a considerable large sac contained many very distinct small balls, analogous to those of the dung of sheep, formed by a fat, unctuous, whitish substance, very different in its appearance from ordinary fat. On the internal surface of this sac were implanted many hairs, which the least force could remove, because they hardly penetrated below the surface. These hairs were black. Many already detached were found crossed in different directions, in the small balls of fatty matter, which was like spermaceti; for it very much resembled the substance into which the fat is changed by maceration.
END OF THE LAST VOLUME.
