78o POPULAR SCIENCE MONTHLY. 



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, f Sir Hum- 

 phry Davy was the first to note, on a voyage to Ceylon, that the 

 temperature of travelers tended to rise in this way, J 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'b. | Observations on Europeans between 

 Khartoum and the equator showed that for those who had been 

 there less than two years the average was 9 9 "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 tempera- 

 ture may bear some relation to the racial pathological predisposi- 

 tions which we have noted, as well as to the liability of the new- 

 comer in the tropics to contract fevers and other zymotic diseases 

 from which the natives and the fully acclimated whites are im- 

 mune. ^ 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 Euro- 

 peans, X the brown skin radiating heat more freely. % The Mon- 

 golian race more nearly approaches the European than does the 

 negro, whose norm is considerably lower.** Dr. Felkinff gives 

 observations to show that the average mouth temperature of six 



* This well-known fact is clearly shown by statistics in Revue d' Anthropologic, second 

 series, v, p. 3*73. 



f Jousset, op. cit., pp. 201, 207, 259, 391. 



I Proceedings of the Royal Society, London, 1814, civ, 1825. Other references in 

 Bulletin de la Societe d' Anthropologic, Paris, 1884, p. 374. 



* Archives de Medecine navale, January, 1878. 



II Bulletin de la Societe d' Anthropologic, 1884, pp. 375 et seq. 



^ Proceedings of the British Association for the Advancement of Science, 1889, p. 787. 



^ The true creole, for example, is immune from yellow fever. 



% Descent of Man, i, p. 233 et seq. 



^ Archiv fiir pathologische Anatomic uud Physiologic und fiir klinische Medicin, cxvi, 

 p. 540. 



% Ibid., cxix, p. 256. Contains many tables of results. 



** Bulletin de la Societe d' Anthropologic, Paris, 1884, p. 380. Jousset affirms the 

 same quite independently, op. cit., p. 383. 



ff Proceedings of the British Association for the Advancement of Science, 1889, p. 787. 



