Page:Popular Science Monthly Volume 48.djvu/862

780 disturbed, the age of puberty being sooner reached. A very important change, which has not perhaps been fully investigated as yet, is a temporary rise of temperature, which often lasts for some time after the individual leaves the tropics. Sir Humphry Davy was the first to note, on a voyage to Ceylon, that the temperature of travelers tended to rise in this way and Dr. Guegnen confirms his conclusions, although he shows that the rise is less than had been supposed. Dr. Maurel concludes that it varies from 0·3 to 0·5. Observations on Europeans between Khartoum and the equator showed that for those who had been there less than two years the average was 99·5°, or nearly a degree above the normal. Those who had been there longer than four years exhibited a lower temperature of 99·1°, still a half degree over the average in Europe.

It is not impossible that these delicate variations of temperature may bear some relation to the racial pathological predispositions which we have noted, as well as to the liability of the newcomer in the tropics to contract fevers and other zymotic diseases from which the natives and the fully acclimated whites are immune. Darwin indirectly hinted at such a solution many years ago, and suggested at the same time a study of the relation of the complexion to immunity from fevers. But no one appears to have followed it up. The recent development of the science of hydrotherapeutics certainly points to this conclusion. Several observers have already noted a permanent difference in the normal mouth temperature of the different races. Glogner has shown that the temperature of the Malay is slightly lower than that of Europeans, the brown skin radiating heat more freely. The Mongolian race more nearly approaches the European than does the negro, whose norm is considerably lower. Dr. Felkin gives observations to show that the average mouth temperature of six