CHAPTER XIII 

 ANIMAL HEAT 



I. Heat production. In the animal body the heat formed 

 originates from the potential chemical energy of the food. 

 In a resting body, in which no energy is used up for ex- 

 ternal work, as much heat is formed as corresponds to the 

 potential chemical energy set free during combustion. 

 Hence the law of conservation of energy holds good also for 

 the transformation of energy in the living body. 



Heat can also be imparted to the body by the taking up of food 

 and drink warmer than the body, but this is of little importance 

 and does not occur regularly. 



In the working body the energy transformed is equal to 

 the heat produced and the external work done. 



The work of the heart, of the muscles of the alimentary canal, 

 and of the respiratory apparatus is not reckoned with the external 

 work, for their work is transformed into heat in the body. 



The unit of heat is the calorie. A calorie is the amount of heat 

 needed to raise i kg of water from o to i C. 



The unit of work is the kilogrammeter^ which is the work 

 done by raising I kg the distance of I meter. One calorie 

 equals 425 kilogrammeters. 



The chemical energy of an oxidizable substance is indi- 

 cated by its heat of combustion, i.e. the heat set free by the 

 complete oxidation of the substance. The following table 

 gives the heat of combustion of a few substances : 



Hydrogen 34-O calories. 



Carbon 8.0 " 



Fat. 9.3 " 



Sugar 3.7 



Starch 4.5 " 



Proteid 5.5 " 



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