CHEMICAL COMPOSITION OF THE BODY 33 



only material for growth and repair, but also a supply of 

 energy. 



Fat is a form in which the body frequently stores fuel 

 food for future uses. If the body has an abundance of food 

 at one time, it need not all be used immediately but may be 

 laid aside as fat, to be called into use at some later time 

 when the body may not be able to secure or to take up the 

 necessary amount of food. 



After a long sickness a patient's eyes are likely to be 

 sunken and the ribs to show through the skin. This is 

 due to the fact that during his illness he has not been able 

 properly to digest and assimilate food, and has been calling 

 upon the stores of fat in his body to support life and furnish 

 him with warmth and energy. 



A tallow candle is made of fat and when it burns, gives 

 out heat. The Eskimo can warm his hands by holding them 

 over the burning candle; but he prefers to eat the candle and 

 let it warm his body through internal oxidation. In this way 

 he does not lose any of the heat. It would be perfectly 

 possible, though expensive, to warm our houses by burning 

 lard, olive oil or butter in our furnaces. So, too, we might 

 burn starches or sugars for the same purpose, or might run 

 an engine with the force they would furnish when burning. 

 Whenever these substances are oxidized, they liberate much 

 energy and if they are oxidized in the body, they liberate 

 this heat and force within it. 



Carbohydrates and fats do not, however, yield equal 

 amounts of energy to the body, the carbohydrates giving 

 us, weight for weight, only about half as much as the fats. 

 Both are composed of the same elements, carbon, oxygen and 

 hydrogen, and it is natural as well as quite worth while to 

 ask why one yields so much more than the other. The 

 answer lies in the relative amounts of carbon which these 

 foods contain; the chemical formula for starch is CeHioOs; 

 for sugar, CeH^Oe; for fat, CsiHio4O9. Now, in the changes 



