In order to observe the organization of the nails advantageously, it is necessary to take those that are very distinct, as those of the great toe, the thumb, &c. We then see evidently that a single lamina occupies the whole of their convex surface. Behind, this lamina exists alone; hence the extreme thickness of the nails at this place. But as we examine towards the front, we see new laminæ successively added to it, on the concave surface; so that the nail becomes successively thicker. These laminæ can be easily raised up layer by layer. The most anterior are the shortest. They often exhibit upon the concave surface of the nail an infinite number of very evident small striæ, all longitudinal and parallel, and which make us attribute to it a fibrous texture. At other times this arrangement is less evident. What is the nature of the laminæ which form the nails? I believe that they are almost precisely the same as the epidermis. What proves it is, 1st, that the most superficial is evidently continued with it by its edges; there is no intermediate agent between them. 2d. I have already observed that the nails are detached, and then regenerated exactly like the epidermis. They have two modes of increase; one in length, when we cut their extremities; the other in thickness, when we detach only a lamina, which is soon formed again. When the whole of the nail comes off, all the portion of the dermis which covers the back of the last phalanx, contributes at the same time to form it anew by its external surface. 3d. There is the same obscurity in the vitality of the nails as in that of the epidermis. No trace of animal sensibility is discoverable in them. The excruciating pain that is experienced when they are pulled out arises solely from the sensibility of the subjacent pulpy texture; it is from the same cause as in pulling out the hair. There is no organic sensibility, no internal circulation and consequently no heat inherent in the texture of the nails; thus the horns of animals are nearly of the same degree of temperature as the atmosphere, whilst some external productions with evident vital forces, though raised up like horns, have a temperature equal to that of the body. Such are the combs of the cock of our country, and those which are more striking of the cock-turkey. Compare these excrescences with those on the feet of these animals, which are horny, and the difference of temperature is evident. 4th. The nails give out when burning a disagreeable odour, analogous to that of the epidermis under the same circumstances; they exhibit then the same phenomena. Their combustion is supported, like that of the epidermis, by an oil of which they contain a great quantity. 5th. If maceration and stewing do not produce upon the nails that want of consistence, that kind of brittleness, if I may so express myself, which they produce upon the epidermis, it appears to be owing only to their greater solidity. 6th. The action of the nitric, sulphuric acids, &c.