TEMPERATURE AND LIFE. 427 



Moist air is a better couductor than dry air, and it is still better if 

 charged with steam. Thus man can easily remain for 10 minutes in 

 a sweating room of dry air at 90° or 100°, but could not endure tbe 

 same length of time in moist air at even a lower temperature. He 

 would soon be overcome in the latter case at dO^ or 100°. That which 

 is true of high temperature is naturally true also of low. Dry air is 

 not so good a conductor as moist, and moist air is inferior to water as 

 a conductor. One can live in air at degrees of cold which would surely 

 be fatal if the environment were a liquid. We have already stated 

 how weak is the resistance of warm-blooded organisms to high degrees 

 of temperature. In fact, in spite of perspiration and exhalations of 

 vapor by the lungs, it is often impossible for the equilibrium to be 

 maintained, and the organism becomes overheated. Its temperature 

 can be increased very little without being fatal. It endures a decrease 

 of 15° or 20"^ in its internal temperature, while an increase of more 

 than 6° or 6^ would be dangerous. If the temperature of man or mam- 

 mal reaches 44° or 46° death results. Birds can exist at a point some- 

 what higher. First comes a period of great excitation and convulsions, 

 from which it falls into a comatose state, followed by death. This 

 result has not yet been elucidated as clearly as desirable. Death 

 under all circumstances is sufficiently complex, but its complexity 

 varies according to its conditions. There are dis-arrangemeuts in the 

 chemistry of the muscles, a portion of which undergoes a change. 

 There are affections of the blood which may be lacking in oxygen 

 though not presenting indications of any iiarticular poison. Notwith- 

 standing Claude Bernard, it is the thermic rigidity and the muscular 

 injury which are most serious. These are of themselves sufficient to 

 cause death, for their effect is to arrest respiration and circulation. 



In conclusion we can say that there is, in the case of heterothermic 

 organisms, great endurance of intense cold, and, to a certain extent, of 

 heat, despite the very marked action of thermic variations upon their 

 organizations. In the case of homeothermic organisms we find moder- 

 ate endurance of low temperature, and very little resistance to an 

 increase of internal temperature. For then a low temperature is accom- 

 panied with much less danger than a high one. The former has to be 

 pronounced to entail death, whereas a slight rise of temperature beyond 

 a certain point will produce immediate and fatal results. 



Between these two classes of organisms there is another group called 

 hibernating animals. These are, for the most part, rodents, which, at 

 the approach of cold weather, make an underground habitation well 

 covered with moss and other substances, where they remain motionless, 

 rolled up like a ball, during the bad season, sleeping during the entire 

 time, torpid, neither eating nor drinking. With these animals the 

 internal temperature becomes very low, following somewhat the ther- 

 mic variations. They scarcely breathe. Their respiratory combustions 

 diminish, and their temperature descends to 20°, 15°, and 10°, and even 



