ACCLIMATIZATION. 781 



hundred negroes between the equator and 10 north latitude was 

 97*8 F., the European normal being 98'6. Higher than either 

 were the Soudanese, whose average was 99. In the European 

 coming to the tropics, therefore, the temporary rise of body tem- 

 perature increases still more the difference between his own and 

 the indigenous normal in most cases. It has, indeed, been sug- 

 gested that this is the cause of malarial fever in the tropics, but 

 the matter has never been fully investigated, especially in its re- 

 lation to other zymotic diseases. 



Among animals the connection between minute variations of 

 body temperature and the liability to contract diseases due to 

 micro-organisms is well established. A fowl, whose normal tem- 

 perature is considerably above that of the horse, the dog, or the 

 rabbit, is immune from splenic fever, to which these other animals 

 are liable ; and yet Pasteur, by reducing its blood heat to their 

 level, by immersing its legs in cold water, was able successfully to 

 inoculate it with the anthrax bacillus.* And other fowls were 

 cured of the fever so contracted by artificially raising their tem- 

 perature to a point at which the bacillus could no longer thrive. 

 For the same reason tuberculosis does not nourish in frogs or 

 other cold-blooded animals, unless their blood temperature is 

 sufficiently raised to permit of its germination. It is too early to 

 assert that the same law will apply to the " traumatic " diseases 

 of the tropics ; but one point is certain, that newcomers in those 

 regions are particularly liable to zymotic diseases during that 

 period when their temperature is most above the native normal ; 

 and that immunity from attack, or at least a more benign form 

 of the disorder, often comes with that fall in temperature which 

 is perhaps the surest sign of true acclimatization. Finally, it 

 will be noted that even when this temperature falls once more to 

 the European normal, it is still higher than that of the natives. 

 And if there were any truth in this theory, the perfect accommo- 

 dation to the environment which the natives of the tropics enjoy, 

 would be attained only when the normal temperature of the Euro- 

 pean had been reduced to their level. But the persistence of phys- 

 iological ethnic traits is a well-known fact; the Hindu to-day, 

 despite his long sojourn in the tropics, has a temperature merely 

 reduced to his own racial normal to reduce it still further to the 

 level of the negro would require ages of time.f 



Acclimatization in this physiological sense, of a gradual ap- 

 proach and approximation to the normal type of the natives, 

 must of necessity be an exceedingly slow process, involving many 

 generations of men. Yet in every respect except of temperature it 



* Button, Evolution and Disease. London, 1890, p. 253. 

 f Jousset, op. cit., p. 382. 



