Race does not change while it remains upon the same soil and under the same natural influences; whereas, it is gradually modified, according to its new position, when it is removed to another place. The physical influences of a region, and of mixture of race, have a distinct manner of acting. By cross-breeding, the features are at once strongly modified in individuals, but especially according to the region in which it takes place. Thus, in Europe, the mixed race is more strongly inclined to the type of the white man; in Soudan, to that of the negro. A type seems to be more readily improved than degenerated. The physical character of a place does not act in detail, but in a general manner, beginning by modifying the complexion more and more in each generation. It acts less quickly upon the hair, and more slowly still upon the features. Cross-breeding is considered the principal modifying agent only because its effects are at once perceptible, but it can explain evident facts only in an imperfect manner. The elevation of a place above the level of the sea has a radical influence upon phthisis. With the design of indicating the regions and the degrees of elevation within which this malady is rare or completely unknown, Dr. Schnepp has made a compilation from a series of meteorological observations, made in the Pyrenees and at Eaux Bonnes, and from analogous documents furnished by travellers who have lived upon the elevated and inhabited plateaux of the old and new world. The document on this subject which he sent to the Academy of Sciences shows that, in the choice of a healthy locality for invalids, people are too exclusively influenced by a warm temperature, disregarding the more formal indications of nature in distributing the maladies of the human race over the surface of the globe. For instance, phthisis exists in the tropical zone. In Brazil, it causes one fifth of the cases of mortality; in Peru, three tenths, and in the Antilles, from six to seven, in every thousand inhabitants. In the East Indies, the greater part of the English physicians report, among the causes of death, two cases from phthisis to every thousand people. In the temperate zones, phthisis is one of the most devastating of diseases. It generally attacks from three to four in every thousand inhabitants. The three countries in which it was not to be found, Algiers, Egypt, and the Russian steppes of Kirghis, have also been invaded by it, although in a smaller proportion, In Algeria, the deaths from phthisis are, to those from other causes, in the proportion of one to every twenty-four or twenty-seven; in Egypt, in the proportion of one to eight. {78}