i 4 6 HUMAN PHYSIOLOGY CHAP. 



One of the most important purposes of the foods we 

 eat is to furnish heat to keep us warm so that all the 

 cells may do their work as they should. The oxidation 

 of fats liberates much more heat than can be obtained 

 from any other food stuff. That is the reason why so 

 much fat and oil is eaten by people living in cold coun- 

 tries. It is really the best food stuff to keep them warm. 

 In warm climates, however, very little fat is eaten. The 

 proteids and carbohydrates, when completely oxidized, 

 are about equally valuable as heat producers ; they lib- 

 erate about half as much heat as the same weight of 

 fat does. 



About ninety per cent of the heat produced daily 

 comes directly from the oxidation of the foods eaten. 

 A small amount comes from the warm substances taken 

 into the body, and from the friction caused by the 

 movement of the blood, the action of the muscles, and 

 from still other sources. 



111. Loss of Heat. The amount of heat produced 

 every twenty-four hours is very great, and yet the 

 temperature of the body remains unchanged. What 

 becomes of it ? About one fourth of the heat may be 

 transformed into mechanical energy and used in doing 

 work. The remaining three fourths is slowly lost ; it 

 keeps up the temperature of the body, and then some of 

 it radiates from the skin into the surrounding air, which 

 is usually cooler than the body. The air we inhale, the 

 water we drink, and many of the foods we eat are cooler 

 than the body, and hence some of the heat is used in 

 raising the temperature of these things. All of the wastes 



