CHAPTER Vn 

 FACTORS INFLUENCING BODY TEMPERATURE 



The body temperature of an animal may be influenced 

 by a number of factors. Those which are more or less 

 directly related to metabolism have been considered in 

 Chapter VI and will therefore be only briefly discussed 

 again here. Metabolism is, of course, the chief source 

 of the heat which keeps the bodies of animals more or 

 less warm; but other influences such as food, insulation, 

 temperature of environment, adaptation to environ- 

 mental rhythms, and glandular or nervous control may 

 also be important. 



Metabolism. — ^In a general way the rate of metabolism 

 of poikilotherms varies directly with the temperature of 

 the environment (Krogh, 1914; Powers, 1923; Hall, 1925) 

 and at suboptimum temperatures the opposite is to some 

 degree true of homoiotherms (Pike, 1923). However, 

 poikilotherms have a slight tendency to adjust their rates 

 of metabolism to temperature changes in the environ- 

 ment. A planarian, if changed from an environment of 

 20 to one of 10 deg. C, at first shows a reduced rate of 

 metabolism, but after two or three weeks returns to about 

 its former rate at 20 deg. C. (Behre, 1918). A turtle 

 which is cooled to 4 to 5 deg. C. shows a check in the 

 gradual decrease in metabolic rate (Baldwin, 1925). 

 Both the planarian and the turtle have a slight tendency 

 to compensate for environmental changes in temperature, 



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