ACTIVITIES OF LIVING BEINGS 31 



taken by a suitable thermometer placed for 

 a few minutes in the arm-pit, varies in a 

 state of health only within a few fractions of 

 a degree above or below 98 Fahr. whether 

 the temperature be taken within the Arctic 

 circle or at the Equator. On the other hand, 

 the temperature of the body of a frog or of a 

 fish varies as the surrounding temperature 

 rises and falls. Such an animal is said to 

 be cold-blooded. The terms cold-blooded 

 and warm-blooded are not scientifically 

 appropriate. A warm-blooded animal, such 

 as a man or a dog, has a temperature that 

 is fairly constant, whereas a so-called cold- 

 blooded animal, like a frog or a fish, has 

 a temperature that varies considerably with 

 the temperature of the medium in which it 

 lives. But if the temperature of the air 

 surrounding a man's body is lower than 98.4 

 F., then the body must be constantly losing 

 heat by radiation and conduction. The 

 questions at once arise : What is the origin of 

 this heat ? By what channels is it lost from 

 the body ? By what arrangement is the 

 temperature kept so uniform ? Are there 



