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.
This old malady becomes more rare as we approach the higher latitudes. It is supposed not to exist at all in Siberia, in Iceland, and in the Faroe Islands. Thus, diseases of the lungs seem to be more rare in certain cold countries than in warm countries. It is also observed that at a certain altitude the number of cases greatly diminish, and even completely disappear. Brockman testifies that phthisis is rare on the plateaux of the Hartz mountains at the height of two thousand feet above the level of the sea; and C. Fuchs, stating the same fact concerning certain elevations in Thuringia and the Black Forest, was the first to advance the theory that phthisis diminishes according to certain altitudes.
Dr. Brüggens, also, has since testified to the infrequency of this disease in the Swiss Alps, at the height of 4500 to 6000 feet in the Engaddine; nor is it found among the monks of the Great Saint Bernard at the altitude of 6825 feet. According to M. Lombard, it completely disappears among these mountains at the height of 4500 feet.
The populous cities of the American continent, which are situated in the tropical zone at an altitude of six thousand feet above the level of the sea, are exempt from lung diseases; although, in the same latitude, phthisis is common in lower regions, This immunity exists on the other hemisphere in the same zone—on the elevated plateaux of Hindostan and the Himalaya. In examining the state of the climate on the heights in which phthisis is seldom or never found, we find there, even on the equator, a medium temperature sufficiently low throughout the year; between twelve and fifteen degrees on the heights below 9000 feet; between three and five degrees on those between 9000 and 12,000 feet.
In the temperate zone it is still lower. But the warmest months upon tropical heights do not vary more than six or eight degrees from the medium temperature. It is the same on the plateaux of the Alps and in Iceland, and is a general and common characteristic of the regions in which phthisis is not found. The deviations below the annual medium, appear even to increase this immunity. If sufficient observations have not been made to decide upon the degree of comparative humidity on the heights above 12,000 feet, we know that the elevation at which phthisis is wanting, is in a hygrometrical condition more nearly approaching saturation than the lower regions, and that the rains are also more abundant there.
It is desirable that the heights of Cévennes, the Pyrenees, the Alps, and, above all, the elevated parts of our Algerian possessions should be carefully studied, with a view to the treatment of lung diseases, which are the great scourge of the human race, and which annually cause the death of more than three millions of its number.