MAINTENANCE OF THE BODY TEMPERATURE 367 



adhered to by birds and mammals are in the same 

 general region, say between 97 and 110. The highest 

 temperatures are those of small birds. It was suggested 

 in Chapter XVI that the salts of the plasma are rem- 

 iniscent of those in the pre-historic sea from which ances- 

 tral forms of life came to land. It may also be suggested 

 that the temperatures so faithfully perpetuated by birds 

 and mammals of the present are those which were im- 

 pressed upon the early organisms by the water in which 

 they lived. It may be argued that if this is so the cold- 

 blooded animals are really the ones which have more per- 

 fectly met the geological conditions of our time. The 

 failure of the homothermous to adjust themselves obliges 

 them to metabolize a great deal more food than would 

 be necessary if they took the temperatures of their 

 environment. The low temperature of fishes does not 

 prevent them from being very active ; on the other hand, 

 we do not find much cerebral capacity in any of the 

 cold-blooded species. 



When we speak of constant temperatures we have 

 always in mind the internal and not the surface condi- 

 tions. The temperature of the human skin cannot be 

 constant since it is influenced by the varying state of 

 the air as well as by the changes in the circulation. 

 The skin temperature approaches that of the blood 

 most nearly when the vessels are locally dilated and when 

 a covering retards the loss of heat to the air. We 

 know that an exposed spot is not proof against frost- 

 bite which shows how the regulating mechanism may 

 be overmatched. 



The clinical thermometer may be used in the mouth, 

 the armpit, or the rectum. Occasionally other localities 

 are utilized or the temperature of the urine may be taken. 

 If the mouth and rectal temperatures are taken at the 

 same time the latter will generally be the higher by about 

 half a degree. The difference is increased when there is 

 deep breathing because of the cooling effect on the 

 whole region about the mouth. Runners who are 



