FATE OF THE FOOD ABSOEBED 385 



" cold-blooded animals," reptiles, amphibia and fishes, do not do 

 so, and their temperature varies with that of the surrounding 

 medium. 



But even in mammals the mechanism for the regulation of 

 temperature is not absolutely perfect, and in every species of 

 animal there is a limit to the power of adjustment. 



Mammals which hibernate become for the time " cold-blooded 

 animals," and lose their power of regulating their temperature. 



The regulation of temperature may be effected either by 

 modifying heat production, or by altering the rate of elimination. 



Heat production is voluntarily modified when muscular 

 exercise is taken during exposure to cold, and involuntarily 

 when muscles are set in action by a shivering fit. There is, 

 however, no evidence of the existence of a special nervous 

 mechanism presiding over heat production in muscle. 



But it is not so much by changes in the rate of heat pro- 

 duction, as by alteration in heat elimination through the skin, 

 that the temperature is kept uniform. The nerves to the 

 cutaneous vessels, and to the sweat glands, are the great con- 

 trollers of temperature. It is through failure of this mechanism 

 under the action of the toxins of micro-organisms that heat 

 elimination is diminished, and the temperature is raised in 

 fevers. 



It is not necessary to assume that there is a special heat 

 regulating nervous mechanism, since the nervous arrangements 

 presiding over the vessels and glands of the skin are capable of 

 immediately responding to change of condition calling for 

 their intervention. 



II. STORAGE OF SURPLUS FOOD 



A. Since bulk for bulk fat has more than twice the energy 

 value of proteins or carbohydrates, it is an advantage to store 

 surplus food as Fat. 



This storage takes place chiefly in three situations: (1) 

 Fatty tissue; (2) liver; (3) muscle. 



1. In Fatty Tissues. In most mammals the chief storage of 

 surplus food is in the fatty tissues. 



That the fat of the food can be stored in them is shown 

 by the fact that the administration of large amounts of fats 



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