Vital Heat of Cold-blooded Animals, 15J) 



ture, that it surpasses what has been observed among animals, 

 excepting those with warm blood, insomuch that, in this point 

 of view, vegetables exist which hold the first rank among liv- 

 ing beings with a low temperature. 



Why do living beings present only two conditions of ex- 

 istence in regard to the degree of their vital heat ? Why are 

 some of a high temperature, while in others it is very low, 

 without any existing which, in their normal state, possess a 

 temperature intermediate between these two extremes ? I am 

 aware that warm-blooded animals, in a state of hybernation, 

 have an inferior vital heat to that which attends their normal 

 condition, and higher than that of cold-blooded animals ; but 

 that does not constitute a normal condition of existence in- 

 termediate to that of warm-blooded animals in their normal 

 state, and that of animals with cold blood. The warm-blooded 

 animal, whose vital heat is diminished while in a state of hy- 

 bernation, enjoys life but imperfectly, and would soon perish 

 if that state were prolonged. It may therefore be established, 

 as a general law of nature, that the vital heat of living beings, 

 whether vegetable or animal, must either be so faint, that it is 

 often impossible to recognise its presence, or so elevated as to 

 approach that degree in which the existence of life, and espe- 

 cially of animal life, becomes impossible. The degree of con- 

 stant heat, which is incompatible with the normal and perma- 

 nent existence of animal life, appears to be about 122° F. (50°. 

 Cent.) ; for the vital heat of birds is so high as 111° F. (44° Cent.) 

 To possess an extreme degree of vital heat^ or almost none^ appears, 

 therefore, to be the law to which all living beings are subjected. 

 The existence of this law is inferred wholly from the fact of its ge- 

 nerality ; for we perceive no reason for its necessity. Living crea- 

 tures with a loxo temperature^ in order to live in their normal con- 

 dition, must necessarily derive heat from the surrounding me- 

 dium ; living heings with a high temperature, on the contrary, in 

 order to live in their normal state, must necessarily lose heat 

 by imparting a portion of what they produce to the medium 

 which surrounds them. The former must, therefore, be placed 

 in a medium warmer than themselves, and the latter in one 

 colder ; for no animal with a high temperature or warm blood 

 can live in a medium equal in warmth to its own, and much 



