TEMPERATURE AND LIFE.* 



By Henry de Yartgny. 



Everything that lives generates heat. Wherever there is life there 

 is simultaneously a productiou and liberation of heat. On the other 

 hand, there exist for ail organic life, animal or vegetable, limits of tem- 

 perature, above or below which life can not be sustained and between 

 which points only can full development be attained. Temperature is 

 therefore an impor;ant element in all life, and it is interesting to con- 

 sider in detail the facts upon which this conclusion rests. We must 

 weigh successively two questions: namely, the generation of heat by 

 organic life, and the influence exerted upon that life by the theometric 

 variations to which it may be subjected— variations which necessarily 

 react upon internal temperature, with different degrees of intensity, 

 however, as wo shall see. 



I. 



Every animal is a source of heat. Tliis is distinctly appreciable in 

 man, birds, and superior organisms in general, and the characteristic 

 temperature of the various members of the animal kingdom presents 

 interesting, although inconsiderable, differences. Birds generate more 

 heat than any other organism, in so far as their temperature is shown 

 to reach a higher point. According to various observers, it varies 

 from 39° to 44° C, while that of man and mammals ranges between 

 370 and 390 C. (98° and 102° F.) 



Man, mammals, and birds are called creatures of equable temperature, 

 homeothermic— that is warm-blooded— animals. By this is meant that 

 their individual temperature is high, that it varies but slightly, and 

 that it does not follow the changes in the surrounding atmosphere. 

 Another class of organisms, representatives of which are never found 

 among birds or mammals, are called heterothermic— cold-blooded- 

 animals; creatures of variable temperature, since, in their normal 

 physiological state, their individual temperature follows closely the 

 changes in the atmosphere about then. The temperature of reptiles, 

 batrachians, fishes, mollusks, Crustacea, insects, etc., is almost identical 



* Translated from tlie Bevue des Deux Mondes, May 1, 1889 ; vol. xciii, pp, 176-201. 



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