376 PHILOSOPHY OF ZOOLOGY. 



HER, and others, on the human body, it appears to vary 

 greatly, being, in the same individual, sometimes positive 

 and at other times negative, and liable to sudden change, 

 upon any quick motion being performed. In making these 

 observations, there is some difficulty in avoiding the effects 

 of friction of the cloth, and other circumstances foreign 

 to the natural state of the body. 



III. ANIMAL HEAT. 



IN every animal there is a certain degree of heat neces- 

 sary to its existence, and the full exercise of its functions. 

 In quadrupeds and birds this heat is considerably great- 

 er, in general, than the surrounding atmosphere, while in 

 fishes and the animals of the inferior classes, it is seldom 

 very different from the temperature of the objects with 

 which they are usually in contact. The ordinary temperature 

 of the human body is rated at between 96 and 98 of F. 

 In the common hen, the temperature is between 10# and 

 104. Those animals whose temperature is high, and not 

 greatly influenced by the changes in the heat of external 

 objects, are denominated warm-blooded animals. Those, 

 on the other hand, whose temperature is greatly influenced 

 by that of surro'unding objects, are termed cold-blooded 

 animals. In both classes, the temperature is regulated by 

 the vital powers of the animals, and limits are assigned be- 

 yond which it is dangerous to pass. The range of warm 

 blooded animals is confined, that of the cold blooded exten- 

 sive. Both, however, are influenced by the same agents, 

 and appear to be governed by the same general laws. 



1. When an animal is exposed to a change of tempera- 

 ture^ some corresponding change likewise takes place in 

 the heat of its body. The propriety of establishing this 

 general law, is sanctioned by the experience of our own 



