LECT. XI. ACTION OF CALORIC. 221 



Dr. John Davy on this point, give only very slight differ- 

 ences. Franklin was the first to observe, that the tempera- 

 ture of his body was -f 35-55 centig. [ =* 96 Fahr.], 

 whilst the air was at + 37-77 centig. [ = 100 Fahr.]. 

 The conclusion drawn from this fact was, that warm-blooded 

 animals had the faculty of remaining in a degree of heat 

 below that of the medium in which they exist. Neverthe- 

 less, it was necessary to ascertain whether, if placed in a 

 temperature much higher than that which is natural to man, 

 the temperature of his body did not undergo some variations. 

 Delaroche and Berger found an increase of 5 centig. [ = 

 9 Fahr.] in the temperature of one of them, who had re- 

 mained for eight minutes in a chamber heated to -4- 86 

 centig. [ = !86-8 Fahr.]. The same experimentalists 

 have repeated their trials upon mammals and birds, and 

 ascertained that the exposure of these animals to a hot and 

 dry air produced an elevation in their temperature, but that 

 it cannot exceed 7 or 8 centig. [ = 12-6 to 14-4 Fahr.] 

 without causing death. 



An elementary knowledge of physics suffices to ex- 

 plain the effects of the exterior temperature on the heat of 

 animals. The formation of aqueous vapour, which con- 

 stantly escapes by the skin of an animal, is a permanent 

 cause of refrigeration for it. This fact explains why in hot 

 and dry air the temperature of the animal is not so high 

 as when the air is loaded with vapour. 



There exists, then, in the animal, a constant source of 

 heat, and a constant cause of refrigeration, and an almost in- 

 variable temperature is maintained, notwithstandingthe vari- 

 ations which take place in the exterior media, whether 

 colder or hotter than itself, since the cause of cooling is 

 more energetic in proportion as the temperature is higher, 

 and vice versa. 



Edwards, tried a great many experiments with the view 



