CHAPTEK VIII 



THE MECHANISMS OF TEMPERATURE REGULATION IN 

 HOMOIOTHERMS 



The preservation of life in a homoiothermal animal 

 requires the maintenance of a constant temperature, 

 though the external and internal conditions may vary- 

 greatly and may tend to warm or cool the body. A 

 variation of a few degrees in the internal temperature 

 of a higher mammal may result in death. Normally, 

 little variation occurs. Such constancy results from the 

 adjustment between characteristic temperature regulat- 

 ing mechanisms which are present in the homoiotherms : 

 heat is produced continuously and rapidly and is dissi- 

 pated at about the same rate. The living organism must 

 adjust heat production and heat loss in such fashion that 

 the temperature of the body cells is maintained near their 

 optimum. Such regulation is termed thermotaxis, or the 

 balance maintained between the two mechanisms: 



1. Kegulation of the loss of heat. This is termed 

 physical heat regulation, or thermolysis. 



2. Eegulation of the production of heat. This is the 

 chemical heat regulation, or ther mo genesis, 



Thermogenesis. — The metabolism of the poikilo- 

 therms is influenced by temperature in such a way that 

 lower temperatures result in low rates of metabolism and 

 high temperatures in high rates. In general the Van't 

 Hoff law for chemical reactions is followed. This is 



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