Page:George Archdall Reid 1896 The present evolution of man.djvu/272

260 Under such conditions, therefore, as formerly obtained in the New World, the evolution of zymotic diseases of the non-malarial type could hardly have occurred; the nutritive supply was insufficient, the human population too scanty, to permit of saprophytic micro-organisms acquiring parasitic habits in relation to man. This à priori conclusion also is amply confirmed by à posteriori considerations, for no evidence is forthcoming to show that zymotic diseases of the non-malarial type were prevalent in the New World before it was infected from beyond its bounds. We may read plenty of accounts which set forth how Spanish, Portuguese, or English adventurers suffered from "calentures," &c., but the diseases mentioned are evidently all malarial in type. Of syphilis there is indeed a tradition that it came to the Old World from the New, but there is no supporting evidence, and the tradition is negatived by the fact that the disease is particularly virulent among New World races, whereas it is particularly mild when attacking some Old World races, such as the Portuguese. The case for yellow fever is stronger; and it may be in the large and, at the time, somewhat densely-populated West India islands this one zymotic disease of a non-malarial type—perhaps it would be more correct to say of a semi-malarial type—did undergo evolution, and that it existed among the native Caribs before the discovery of America; but it is probable that even this disease was imported from the Old World. "The first reliable accounts of yellow fever date from the middle of the seventeenth century; they tell of the importation of the disease from place to place, and from island to island." It is significant that the disease prevails on the West Coast of Africa, and that more than all other