BODY HEAT 51 



been arrested at an early stage, with the consequence 

 that they can only to a small degree maintain their 

 activity, regardless of what the surrounding temperature 

 may happen to be, and in some cases at least, such as 

 Echidna, are compelled to resort to the device of hiberna- 

 tion and a suspension of all attempts at bodily activity 

 when exposed to great cold. Even in some of the 

 higher mammals the heat-regulating mechanism is not 

 in proper working order at the time of birth, and such 

 animals perish from cold if separated from their mothers. 

 In the case of puppies, for instance, which of course 

 are born blind, the power of maintaining the temperature 

 of the body does not arise until sight is attained. Babies 

 who are born prematurely, also, are unable to control 

 their temperature, and would perish were it not for the 

 aid of an incubator or some other device for keeping 

 them warm. Even in normal infants the power of regu- 

 lating heat production and loss is very imperfect during 

 the first week ; hence the importance of warmth to the 

 newly-born baby. 



Now, although all the higher animals have developed 

 the power of maintaining their bodies at a constant 

 temperature, it is an interesting fact that the exact point 

 at which evolution has fixed it to be maintained is by 

 no means the same in all. In man it may be taken as 

 a temperature of 98*6 F., the range of internal tempera- 

 ture in health being from 96'8 F. to 100 F. ; but in 

 most other mammals it is more nearly 102 F., whilst 

 in birds it is as high as 107 F. Why these differences 

 exist it is difficult to explain. All one can say is that 

 a temperature of 98*6 F. is the tune to which the 



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