18 RESPIRATION. 



bonic acid within the body, must give out exactly as 

 much heat as if it had been directly burnt in the air or 

 in oxygen gas ; the only difference is, that the amount 

 of heat produced is diffused over unequal times. In 

 oxygen, the combustion is more rapid, and the heat 

 more intense ; in air it is slower, the temperature is not 

 so high, but it continues longer. 



It is obvious that the amount of heat liberated must 

 increase or diminish with the quantity of oxygen intro- 

 duced in equal times by respiration. Those animals 

 which respire frequently, and consequently consume 

 much oxygen, possess a higher temperature than others, 

 which, with a body of equal size to be heated, take into 

 the system less oxygen. The temperature of a child 

 (102) is higher than that of an adult (99-5). That 

 of birds (104 to 105-4) is higher than that of quad- 

 rupeds (98-5 to 100-4), or than that of fishes or am- 

 phibia, whose proper temperature is from 2-7 to 3-6 

 higher than that of the medium in which they live. All 

 animals, strictly speaking, are warm-blooded ; but in 

 those only which possess lungs is the temperature of the 

 body quite independent of the surrounding medium. (5) 



The most trustworthy observations prove that in all 

 climates, in the temperate zones as well as at the equa- 

 tor or the poles, the temperature of the body in man, 

 and in what are commonly called warm-blooded animals, 

 is invariably the same ; yet how different are the cir- 

 cumstances under which they live ! 



The animal body is a heated mass, which bears the 

 same relation to surrounding objects as any other heated 



