Pruner Bey has insisted strongly upon the thickness of the cutaneous layers, and especially upon that of the dermis in the Negro. Is not this thickness the natural consequence of the flow of nutritive principles brought by the blood, which is incessantly passing to the surface of the body to keep up the perspiration? It has long ago been remarked that the Negroes and other races inhabiting hot countries perspire much less than the inhabitants of temperate climates. This is accounted for by the preceding facts. The blood, which is constantly brought to the surface and into the cutaneous organs, does not flow so copiously in the sudoriparous glands, which are deeply buried beneath the adipose tissue. Between _transpiration_ and _perspiration_, in consequence of the position of the organs, a real equilibrium should exist. Probably, one of the difficulties of acclimatisation arises from the fact that the proportional activity of these two functions has to be changed when we pass from a temperate to a tropical climate, or _vice versa_. The researches of Krause show that the body of a European contains more than 2,281,000 sudoriparous glands. The total volume of all these small organs would amount to about 40 cubic inches. A sudden change in functions could not therefore be unimportant. Moreover, the sebaceous glands, which are smaller but more numerous than the sudoriparous, participate in this change, which can only result in a serious shock to the organism. The villosities are either very rare or absolutely wanting on the surface of the body of a Negro, except some parts which in man are always covered with hair. On the other hand, the glandular cutaneous covering is highly developed in his case. Both these facts may also be referred to the same cause, and are explained by the balancing of connected organs. The blood, when brought to the surface of the body, abandons the _bulbs of the hair_ which are too deeply planted; but, for the same reason it flows into the sebaceous glands, which are situated near the surface. It easily follows that the former suffer atrophy, and the latter experience an exceptional development. This development accounts for the exaggerated odour which is peculiar to the Negro. It is known that a slave-ship may be recognised by this smell. But African populations are not the only ones which are characterised in this manner. Humboldt informs us that the Peruvians distinguish the odour of a native, a white, and of a negro, calling them _posco_, _pezuna_, and _graïo_. Amongst ourselves, every individual has his own peculiar odour, which is easily detected by the delicate sense of smell of the dog.