The nails have in the fœtus a very considerable consistence, whilst the skin is still pulpy; but their tenuity is then extreme. But they thicken and acquire greater consistence as the fœtus increases in size. They have not at birth a length proportionable to what they are afterwards to have. They do not extend beyond the ends of the fingers which are often much the longest; so that it is not till after birth that they are bent over and exceed the fingers in length, for both of these would be useless in the womb of the mother, as there is nothing there for the fœtus to seize upon. Their transparency allows us evidently to see, at the moment of birth, first the black colour of the blood which before circulated in the arteries, and then the vermilion colour which respiration suddenly imparts to it. As we advance in age, the nails grow in the same proportions as the epidermis, but they have nothing peculiar in their growth. In old people they become extremely thick. These organs experience during life those diseases only which are analogous to those of the epidermis. These are excrescences, augmentations of size, &c. and other productions, the texture of which is precisely the same as that of the nail, and in which there is neither more sensibility, nor more circulation, nor more heat, nor more life; a remarkable character which distinguishes them from those tumours which arise upon the other organs with very active vitality, as upon the skin, the muscles, &c. tumours the texture of which is very different from that of the organs which have produced them, and which most usually have properties entirely different. But the epidermoid excrescences are in every respect analogous to the epidermis. PILOUS SYSTEM. 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.