CHEMICAL EFFECTS OF RESPIRATION. 305 



the increased temperature, which all animals, but 

 more especially those designated as luarm-blooded^ 

 usually maintain above the surrounding medium. 

 The uniform and exact relation which may be 

 observed to take place between the temperature of 

 animals and the energy of the respiratory function, 

 or rather the amount of the chemical changes in- 

 duced by that function, affords very strong evidence 

 in favour of this hypothesis. The coincidence, in- 

 deed, is so strong, that notwithstanding the objec- 

 tions that have been raised against the theory 

 founded upon this hypothesis, from some apparent 

 anomalies which occasionally present themselves, 

 we must, I think, admit that it affords the best 

 explanation of the phenomena of any theory yet 

 proposed, and that, therefore, it is probably the 

 true one. 



The maintenance of a very elevated temperature 

 appears to require the concurrence of two con- 

 ditions ; namely, first, that the whole of the blood 

 should be subjected to the influence of the air, 

 and, secondly, that that air should be presented to 

 it in a gaseous state. These, then, are the circum- 

 stances which establish the great distinction be- 

 tween warm and cold-blooded animals ; a distinc- 

 tion which at once stamps the character of their 

 whole constitution. It is the condition of a high 

 temperature in the blood which raises the Quadru- 

 ped and the Bird to a rank, in the scale of vitality, 

 so far above that of the Reptile : it is this which 

 places an insuperable boundary between Mam- 

 malia and Fishes. However the warm-blooded 

 Cetacea, who spend their lives in the ocean, may 

 be found to approximate in their outward form, 



VOL. II. X 



