The epidermis has a property very distinct from those of most of the other systems; it is that of being reproduced when it has been removed. It grows anew and is formed again with an appearance exactly similar to what it first exhibited; it is that which makes it differ from all the other systems, as the cellular, which throw out vegetations when they are laid bare, but which are only reproduced in an irregular manner, and wholly different from their natural state. How is the epidermis thus reproduced? Is it the pressure of the atmospheric air which renders the external surface of the skin callous? Is it the air, which, by combining with the products which escape from this surface, forms a new compound? I know not. What is certain is, 1st, that this production is wholly different from that of the internal organs; 2d, that it cannot take place except upon the skin, and that the fine pellicle that covers all the other cicatrized parts, after a wound with loss of substance, does not resemble it at all and presents even a texture wholly different. Thus this pellicle is not raised up by the different means which raise the epidermis; thus it often becomes the seat of acute sensibility which is never the case with the epidermis. This is what takes place especially in changes of weather, a time in which the cicatrices become, as we know, very painful; I have often observed, that not only the interior, but the pellicle even of the cicatrix are then sensible. Besides, when this pellicle is formed, red blood vessels evidently penetrate it, whilst nothing similar is observed in the formation of the epidermis. It is this faculty of reproduction which is put in action in many epidermoid excrescences, as in corns, and callosities which have nothing in common but the name with those which form the edge of fistulas, &c. All these excrescences are insensible, without vessels or nerves, of the same consistence and the same colour as the epidermis; they are often removed from it and afterwards formed again. It appears that external pressure has much influence upon their development; too narrow shoes and the solid bodies which are used on the hands of smiths and other workmen are the frequent cause of them. I preserved a great part of the skin of a man who died at the Hôtel Dieu, and his epidermis, which was treble the thickness from his birth and even in the womb of his mother, that it is in the ordinary state, had been subject during his life to a continual desquamation which made the whole of it appear as if covered with herpes, though nothing similar to this affection existed upon the dermis, which was perfectly sound. The face alone was exempt from this defect of conformation.