Do not ships, in which men live crowded together for months under very unsatisfactory sanitary conditions, develop deleterious principles, to which the crews become accustomed by degrees, but which are, nevertheless, capable of producing the most serious affections in the midst of surrounding populations, which, till then, had been in a flourishing condition. Have we here one of those phenomena to which, according to Darwin, we must attribute the terrible mortality and increasing sterility of the Polynesian races? Among the diseases introduced by European sailors, ought we not to reckon phthisis, which is said to have become epidemic, as well as hereditary, in those islands? The probabilities seem to me to be in favour of an answer in the affirmative. Neither land nor sky have changed in these archipelagoes since the time of their discovery, and yet the Polynesian Islanders disappear with a terrible rapidity, whilst their mixed races and even pure-blooded Europeans show a redoubled fertility—a double contradiction given by facts to autochthonic doctrines. It is not always easy to determine, in judging of the more or less deleterious action of given conditions of life, what should be attributed to normal conditions, and what is the result of accidental vitiating elements. The soil, cold, heat, dryness, or humidity of a country are not all. The difference presented from the point of view of acclimatisation by the two hemispheres is a striking example. The hot regions of the southern hemisphere are, as a rule, more accessible to white races than those in similar latitudes in the northern hemisphere. From 30 to 35 degrees of N. lat. we find Algeria, and especially the southern part of the United States, which present serious difficulties against our acclimatisation. In the same latitude of the southern hemisphere, lie the southern portion of the Cape and New South Wales, where all European races prosper almost immediately. M. Boudin’s calculations give the differences exactly. He has found that the mean mortality of French and English armies was about eleven times greater in our hemisphere than in the southern hemisphere. Struck by this contrast, M. Boudin endeavoured to discover its cause, and found that it lay in the greater or less frequency and gravity of marsh fevers. North of the equator these fevers may be traced in Europe as far as the 59th deg. of latitude. In the south they rarely pass the tropics, and often cease at an even smaller distance. Tahiti, which is only 18 deg. from the geographical equator, and almost beneath the thermal equator, is free from them. In the southern hemisphere, the mean annual number of cases of fever in the united English and French colonies was 1·6 in 1000; in the northern hemisphere it was 224·9 in 1000.