340 THE VITAL FUNCTIONS. 



against the theory founded upon this hypo- 

 thesis, from some apparent anomaUes 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 tempe- 

 rature appears to require the concurrence of two 

 conditions ; namely, first, that the whole of the 

 blood should be subjected to the influence of the 

 air, and, secondly, that that air should be pre- 

 sented to it in a gaseous state. These, then, are 

 the circumstances which establish the great dis- 

 tinction between warm and cold-blooded animals ; 

 a distinction which at once stamps the character 

 of their whole constitution. It is the condition 

 of a high temperature in the blood which raises 

 the quadruped 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 mammalia and fishes. However the 

 warm-blooded Cetacea, who spend their lives 

 in the ocean, may be found to approximate 

 in their outward form, and in their external 

 instruments of motion, to the other inhabitants 

 of the deep, they are still, from the conformation 

 of their respiratory organs, dependent on another 

 element. If a seal, a porpoise, or a dolphin 

 were confined, but for a short time, under the 

 suiiace of the water, it would perish with the 



