THERMAL PHENOMENA OF THE BODY 191 



the body remains nearly constant, regardless of changes in 

 the temperature of the air around it. 



We have only to appeal to experience to see that this is 

 not the way in which lifeless matter generally behaves; a 

 stone, the earth, a piece of iron is warmer on a warm day 

 and colder on a cold day; in general, lifeless things take the 

 temperature of the medium in which they are placed, and this 

 is one of the fundamental principles of physics. Nor do most 

 living things act differently; the temperature of a plant or 

 a tree, of an earthworm, a frog, a turtle, a snake, does not 

 differ greatly from that of its surroundings. It is only birds 

 and mammals which show this remarkable power of maintain- 

 ing an approximately constant body temperature notwith- 

 standing wide limits of change in that of the surrounding air. 

 Such animals are known as warm-blooded because they are 

 usually warmer than surrounding objects; those animals 

 which do not thus maintain a constant temperature, on the 

 other hand, are known as cold-blooded. 1 



It is clear that the power to maintain a constant body 

 temperature is of the utmost importance in enabling an ani- 

 mal to counteract the varying conditions of climate. Were 

 it not for this power, man would be a hibernating animal; 

 with the coming of winter all his activities would gradually 

 be slowed down and, long before our rivers and ponds had 

 begun to freeze, all business, industrial life, and intellectual 

 life would come to a standstill; it would not be possible 

 for the human race to people every zone of the earth the 

 shores of Alaska or Iceland as well as the banks of the 

 Ganges or the Amazon. 



5. The temperature of the body not absolutely constant. 

 The term " constant " as applied to the temperature of 



1 A cold-blooded animal exposed to a temperature of 99 F. is as warm 

 as a warm-blooded animal. Such animals are so called because they usually 

 feel colder when handled than do warm-blooded animals ; but this is merely 

 because the temperature of the air (which is also their temperature) is usually 

 lower than the temperature of warm-blooded animals. 



