This is the greatest alteration that the atmosphere has made on man, and yet this is only superficial. The colour of the skin, hair, and eyes, varies solely according to the influence of climate. The other changes, such as that of size, features, and the quality of the hair, do not seem to depend on this cause alone, for among the Negro race, the greatest part of whom have frizzled wool on their heads, a flat nose, and thick lips, we meet with whole nations with long and real hair, and regular features. Again, if we compare, among the white race, the Dane with the Calmuck Tartar, or only the Finlander with the Laplander, who are so near each other, we shall find as much difference between them, with respect to size and features, as there is among the Negroes; consequently we must subjoin some other cause to that of the climate to account for these alterations, which are stronger than the former. The most general and direct cause is the quality of the food, for it is principally through the aliments that man receives the influence of the soil which he inhabits, the air and atmosphere acting more superficially. While the latter alter the external surface by changing the colour of the skin, food acts upon the internal form by its properties, which are constantly relative to those of the earth by which it is produced. Even in the same country we find strong differences between men who occupy the high lands, and those who live in the low. The inhabitants of the mountains are always better made, more spirited, and handsomer than those of the valley: therefore, in countries far distant from the original climates, where herbage, fruit, grain, and the flesh of animals, differ both in quality and substance, the men who feed on them must undergo greater changes. These impressions are not suddenly made. Time is required for man to receive the tincture of the atmosphere, and still more for the earth to transmit its qualities to him. Ages, joined to a constant use of the same nutriment, is necessary to influence the form of the features, the size of the body, the substance of the hair, and to produce those internal alterations which, being afterwards perpetuated by generation, have become the general and constant characters, by which the races, and even the different nations, which compose the human race, are distinguished.