244 ANIMAL HEAT. 



only a slight degree, even in extremes of external tem- 

 perature ; that it falls slowly in passing from hot to cold 

 climates, and rises more rapidly in returning towards the 

 torrid zone : but that these changes in the temperature of 

 the body, are more considerable in some individuals than 

 in others. 



The temperature maintained by Mammalia in an active 

 state of life, according to the tables of Tiedemann and 

 Rudolphi, averages 101. The extremes recorded by them 

 were 96 and 106, the former in the narwhal, the latter in 

 a bat (Yespertilio Pipistrella). In birds, the average is as 

 high as 107; the highest temperature, 111-25, being in 

 the small species, the linnets, etc. Among reptiles, Dr. 

 John Davy found, that while the medium they were in was 

 75, their average temperature was 82-5. As a general 

 rule, their temperature, though it falls with that of the 

 surrounding medium, is, in temperate media, two or more 

 degrees higher ; and though it rises also with that of the 

 medium, yet at very high degrees it ceases to do so, and 

 remains even lower than that of the medium. Fish, 

 insects, and other Invertebrata present, as a general 

 rule, the same temperature as the medium in which they 

 live, whether that be high or low ; only among fish, the 

 tunny-tribe, with strong hearts and red meat-like muscles, 

 and more blood than the average of fish have, are gene- 

 rally 7 warmer than the water around them. 



The difference, therefore, between what are commonly 

 called the warm- and the cold-blooded animals, is not one 

 of absolutely higher or lower temperature ; for the animals 

 which to us, in a temperate climate, feel cold (being like 

 the air or water, colder than the surface of our bodies), 

 would, in an external temperature of 100, have nearly the 

 same temperature and feel hot to us. The real difference 

 is, as Mr. Hunter expressed it, that what we call warm- 

 blooded animals (birds and Mammalia), have a certain 

 " permanent heat in all atmospheres," while the tempera- 



