Page:Popular Science Monthly Volume 48.djvu/744

672 absence of crossing, as among the Jews in the Bourbon Islands, with the Boers in South Africa, and in many parts of South America.

The physical elements of climate, ranged in the order of their importance, are humidity, heat, and lack of variety.

Heat by itself, when unaccompanied by excessive humidity, does not seriously affect human health except when unduly extended. The ranges of temperature to which the human body may become accustomed are very broad, so that the limitations to the dispersion of the race seem to be set by the food supply rather than the degree of heat or cold. All authorities agree, therefore, that the regions where acclimatization is most difficult are to be found in the areas of excessive humidity, or, roughly, where there is the maximum rainfall. For this reason the successful examples adduced in favor of the view that acclimatization in the tropics is possible, should always be examined in the light of this consideration.

A traveler in northern Africa has noted this in his observation, that "where there is water and something can grow, there the climate is murderous; where the climate is healthy, there is no water and nothing can grow." In this sense, the boasted acclimatization of the French in Algeria is merely accommodation to one element of climate, after all. With this limitation it will be generally conceded that the success of the French in their African possessions along the Mediterranean is assured. The mortality of soldiers and sailors in Algeria was seventy-seven