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.