244 APPLIED PHYSIOLOGY 



When warm weather comes again, their respiration and 

 temperature rise to the natural point, and the animal re- 

 sumes its former condition, but is thin from the oxidation 

 of its fat and albumin during his long sleep. The dormant 

 state during the winter is called hibernation. 



434. Cold-blooded animals. In frogs and snakes, oxi- 

 dation is not sufficient to raise their temperatures much 

 above that of the surrounding air. So they feel cold to 

 the touch, and are called cold-blooded. On warm days 

 they do not lose heat so rapidly, and more heat is retained 

 within their bodies, and thus they become more active. 

 When cold weather comes on, they cannot produce enough 

 heat to enable them to move, but they lie unconscious 

 until warm weather comes again. 



Insects cannot produce enough heat during winter to 

 enable them to fly about, so they remain apparently life- 

 less until the warm weather comes again. 



SUMMARY 



1. The heat developed by oxidation is distributed through 



the body by the blood so that everywhere it has a 

 temperature of 98.5 degrees. 



2. The sensations of heat and cold are caused by the 



blood circulating in the skin. If little circulates, 

 we feel cold; while if much circulates, we feel 

 warm. 



3. An increased quantity of food, oxygen, or exercise 



increases the amount of heat produced in the body. 



4. Heat is given off by contact of the skin with the cold 



air and by means of the perspiration. 



5. A temperature of about 70 degrees in a room is the 



most comfortable. 



