CHAPTER XXVII 

 THE MAINTENANCE OF THE BODY TEMPERATURE 



One of the most impressive examples of coordination 

 is afforded by the associated mechanisms which so suc- 

 cessfully preserve the human body temperature from 

 violation. Summer and winter, indoors and out, in 

 the polar regions and in the Sahara, it seems independent 

 of external conditions. A discussion of the facts has 

 been postponed to this time because almost all the 

 other divisions of our science are needed as a founda- 

 tion. The manner of working of the nervous system 

 with its receptors and effectors, the nature of the con- 

 tractile process in skeletal muscle, the government of 

 the circulation, and the factors in metabolism must all 

 be in mind. 



Most animals do not have this wonderful ability to 

 hold themselves to a constant temperature. Birds 

 and mammals generally possess the power and we indi- 

 cate it when we- call them warm-blooded. Speaking 

 accurately, we do not mean so much to emphasize their 

 warmth as the constancy of their internal state. If a 

 fish and a duck are both swimming in water having a 

 temperature of 103F., the two may have the same in- 

 ternal temperature. But if the water cools down the 

 fish will passively submit to a parallel cooling while the 

 duck will be about as warm as before, so far as its deeper 

 tissues are concerned. When we call the fish a cold- 

 blooded animal we mean that it takes very nearly the 

 temperature of its surroundings. 



In the interest of precision we may substitute for 

 warm-blooded the word homothermous, which means hav- 

 ing a uniform temperature. The standards so strictly 



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