CHAPTER XXXI 

 THE REGULATION OF TEMPERATURE 



" Where hot and cold, and dry and wet 

 Strive each the other's place to get." PRIOR. 



ONE of the most striking phenomena in the life of man and of 

 the hot-blooded animals generally is the remarkable constancy 

 of the temperature maintained in spite of the variations of tem- 

 perature to which they may be subjected. This is a fact which 

 did not escape the attention of the ancients,* who thought out 

 many weird and wonderful explanations. Even well on in the 

 nineteenth century, text-books echoed the idea of Haller (1757) 

 that animal heat arose mainly from the friction of the blood in 

 the vessels. 



The mammal or the bird may travel from the arctic regions 

 where the external temperature may be at - 53 C. to the tropics 

 at 53 C. without much increase in body temperature. Contrast 

 this freedom from variation with the continuously changing 

 temperature of the cold-blooded animal as the temperature of its 

 environment changes. 



TABLE LV. 



Within natural limits, the temperature of the cold-blooded animal 

 is usually about 1 C. above that of its environment. It is 

 interesting to note that those animals which hibernate become 

 for the time as if cold-blooded. The evolutionists postulate that, 

 as all animals were once marine cold-blooded organisms, the 

 ancestors of the warm-blooded animals must have crawled out 



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