Part 41

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 fœtus 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.

ANALYTICAL TABLE OF CONTENTS.

VOLUME FIRST. PAGE.

Preface by the Translator. 5

Preface by the Author. ib.

GENERAL OBSERVATIONS.

Of Animate and Inanimate Beings.—Of their Laws.—Of the Sciences which treat of their Phenomena. 9