20 UNIFORM TEMPERATURE OF THE ANIMAL BODY. 



bine with this oxygen must be increased in the same 

 ratio. 



It is evident, that the supply of the heat lost by cool- 

 ing is effected by the mutual action of the elements of 

 the food and the inspired oxygen, which combine to- 

 gether. To make use of a familiar, but not on that 

 account a less just illustration, the animal body acts, in 

 this respect, as a furnace, which we supply with fuel. 

 It signifies nothing what intermediate forms food may 

 assume, what changes it may undergo in the body, the 

 last change is uniformly the conversion of its carbon into 

 carbonic acid, and of its hydrogen into water ; the un- 

 assimilated nitrogen of the food, along with the unburned 

 or unoxidized carbon, is expelled in the urine or in the 

 solid excrements. In order to keep up in the furnace 

 a constant temperature, we must vary the supply of fuel 

 according to the external temperature, that is, according 

 to the supply of oxygen. 



In the animal body the food is the fuel ; with a proper 

 supply of oxygen we obtain the heat given out during 

 its oxidation or combustion. In winter, when we take 

 exercise in a cold atmosphere, and when consequently 

 the amount of inspired oxygen increases, the necessity 

 for food containing carbon and hydrogen increases in the 

 same ratio ; and by gratifying the appetite thus excited, 

 we obtain the most efficient protection against the most 

 piercing cold. A starving man is soon frozen to death ; 

 and every one knows, that the animals of prey in the 

 arctic regions far exceed in voracity those of the torrid 

 zone. 



