GENERAL METABOLISM OF THE BODY. 



A. EXCHANGE OF ENERGY. 



As already indicated (p. 254), the energy exchanges of the 

 body as a whole are determined by the chemical changes 

 in the muscles. Further, the temperature of the body must 

 be maintained at a level at which these chemical changes 

 can go on. For this purpose heat must be produced to 

 compensate for cooling. It will be shown later (p. 272) 

 that the rate of heat production is influenced by the 

 amount and nature of the food taken. Hence the energy 

 requirements depend upon : — 



(1) Muscular activity ; 



(2) The rate of cooling, i.e. the amount of heat that 

 must be produced ; 



(8) The food taken. 



Before considering the influence of these factors, the 

 lowest rate of metabolism compatible with the maintenance 

 of life must be investigated. 



I. The Basal Metabolism. 



The basal, or, as it might perhaps better be called, the 

 standard metabolism, is the rate of metabolism necessary to 

 maintain life when the three factors mentioned above are 

 reduced to a minimum. 



The factors of outstanding importance in determining the 

 basal metabolism of an animal are (1) size and (2) age. 



1. Size. — The variation in size is in proportion, not to the 

 weight but to the surface, i.e. the rate of cooling. This 

 is shown by comparing the basic energy expenditure of 

 animals of different size. 



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