COLD-BLOODED AND WARM-BLOODED ANIMALS 351 



tion, or is made necessary by the increase in surface by 

 foldings. 



Cold-blooded and warm-blooded animals. — By cold- 

 blooded animals we mean those in which the temperature 

 of the blood is only slightly higher than that of the sur- 

 rounding enwonment. These animals feel cold to the 

 touch, as they are of lower temperature than our bodies. 

 This cold-blooded condition is dependent upon the amount 

 of oxidation which takes place in the body, and fishes, 

 frogs, and reptiles have a slower rate than that of birds 

 and man. The higher temperature of birds and mammals 

 is evidently due to the fact that the greater perfection of 

 the respiratory apparatus permits a more rapid exchange 

 of oxygen and carbon dioxide in these animals than in the 

 cold-blooded forms. As a rule, cold-blooded animals are 

 more sluggish in their movements than warm-blooded ones. 



