Page:Popular Science Monthly Volume 25.djvu/410

398 character. In France the ponds of the Dombes and the mouth-country of the Charente were, till recently, no less dangerous. Life in great cities also seems to exercise a special influence on reproduction. Boudin could not find any pure Parisians who could trace the residence of their ancestors in the city back for more than three generations. In Besançon the "old families" generally die out in not quite a hundred years, and are replaced by families from the country; and the same is, to a greater or less extent, the case in London, Berlin, and other large cities.

Has it been proved that on ships, where men are crowded together for months under conditions incompatible with health, particular disorders are developed, to which sailors may, indeed, gradually accustom themselves, but which are apt to mature into fatal maladies among people hitherto in perfect health? Can we, as Darwin suggests, ascribe to such circumstances the fearful mortality and the diminishing fruitfulness of the Polynesian races? Does the consumption which has become epidemic and hereditary in those islands belong to the diseases that have insinuated themselves there by the aid of European sailors? Neither the land nor the sky has changed since the Polynesian archipelagoes were discovered; yet the aboriginal population is diminishing at a really frightful rate, while its bastard offspring and the pure Europeans are increasing rapidly.

To what extent the more or less pronounced dangerousness of a locality is affected by normal conditions or by casual injurious influences is not always easy to estimate. The character of the soil, a higher or lower temperature, dryness, and moisture, are not all that determine the character of a country. We have evidence of this in the fact that the process of acclimatization is not equally easy in both hemispheres. The white races fare much better in the hot countries of the southern hemisphere than in the corresponding latitudes of the northern hemisphere. Between the thirtieth and thirty-fifth parallels of latitude lie Algiers and a part of the United States—regions in which the acclimatizing of Europeans is attended with great difficulties. In the southern hemisphere, the southern part of the Cape Colony and New South Wales lie between the same parallels, and in those countries white men thrive. French and English troops exhibit a rate of mortality eleven times as great in the northern as in the southern hemisphere—a striking difference, which appears to depend upon the greater frequency and intensity of miasmatic fevers. North of the equator these fevers reach in Europe to the fifty-ninth degree of latitude, while south of the equator they seldom extend beyond the tropic and usually do not reach it. Tahiti lies under the eighteenth degree of south latitude, and is free from fevers. French and English troops stationed in the southern hemisphere afford a mean of 1·6 per thousand sick with fever annually, while among those stationed in the northern hemisphere the proportion of fever-sick is 224 per thousand.