562 TEMPERATURE OF 



It has been known since the time of Linnaeus 

 and Dr. Black, that all the higher orders of ani- 

 mals are warm-blooded ; that they have a double 

 heart and a double circulation, by one of which 

 their blood is distributed throughout the lungs, 

 where it is exposed to the atmosphere ; and by 

 the other, sent throughout the system, that the 

 breathing apparatus of birds is larger, in propor- 

 tion to the size of their bodies, than in any other 

 description of animals, extending through all the 

 cavities of the abdomen, and even of the bones; 

 that they consume more oxygen, generate more 

 carbonic acid, and have a higher mean tempe- 

 rature. 



Next to birds, mammiferous animals have the 

 largest organs of respiration. And although 

 confined to the thorax, they consist of innume- 

 rable cells that present a vast extent of surface 

 to the atmosphere. The consequence of which 

 is, that many of them are capable of maintaining 

 their temperature in the coldest parts of the world. 

 Accordingly, it will be seen by glancing over the 

 following Tables, that the mean temperature of 

 birds varies from 105 to nearly 113F. which is 

 about 28 above that of the tropical regions; 

 while in mammalia it varies from 96 to 106 

 in their active and healthy state. But if we 

 descend to the lower orders of air-breathing ver- 

 tebrated animals, such as Chelonians, Saurians, 

 Ophidians, and Batrachians, in which the heart 



