CHEMICAL EFFECTS OF RESPIRATION. 155 



furnace with air ; and the trachea is the chimney, through 

 which the carbonic acid which is the product of the com- 

 bustion escapes.'* 



465. Animal Heat. That animal heat depends on the 

 process of respiration, and that the temperature, whether 

 higher or lower, depends at least in some degree, on the 

 quantity of oxygen consumed, there is good reason to 

 suppose. The uniform relation which may be observed 

 between the. temperature of animals, and the energy of 

 the respiratory functions, affords a very strong presump- 

 tion that this is the case. 



468. It is true that many objections have been brought 

 against this theory, and yet no other hypothesis has 

 been offered which can be supported by so many con- 

 current facts as this. We find as a universal truth, that 

 all hot-blooded animals consume, or vitiate, large quan- 

 tities of air by respiration, and that the whole mass of 

 blood in these is exposed to the action of the atmosphere, 

 in a gaseous form. Whereas the cold-blooded tribe de- 

 pend for respiration on the minute portions of air the 

 water contains, or are so constructed that only half of 

 their blood is exposed to atmospheric influence. These 

 circumstances have already been noticed and explained 

 in the account we have given of comparative circulation 

 and respiration. 



467. Warm Blood in Whales. We find that when ani- 

 mals have all the habits of fish, and spend their lives 

 among the ice of the northern oceans, they still have warm 

 blood, if their organs of respiration are so constructed 

 as to expose the whole mass of circulating fluid to the 

 influence of pure Atmospheric air. Thus the whales, 

 and dolphins have the breathing apparatus of the mam- 

 malia, to which class of animals they belong, and like 

 all the other members of this class have hearts with two 

 ventricles, and a double system of circulation; and 

 although they are constantly exposed to the temperature 

 of the sea, that of their systems is similar to the other 



In what respects are the effects of respiration similar to those of ordi 

 nary combustion ? What reason is there to believe that animal temper 

 ature depends on the quantity of air used in respiration. 



