A STUDY OF FOODS AND DIETARY 345 



Per cent. Per cent. 



Oxygen, about 65.00 .Sodium, about 0.15 



Carbon, about 18.00 Chlorine, about 0.15 



Hydrogen, about 10.00 Magnesium, about 0.05 



Nitrogen, about 3 . 00 Iron, about . 004 



Calcium, about 2.00 Iodine ] 



Phosphorus, about 1 . 00 Fluorine } Very minute traces. 



Potassium, about 0.35 Silicon j 



Sulphur, about 0.25 



Each of these elements will be found in the list of chemical 

 elements given in Art. 84. The oxygen, carbon, hydrogen, 

 and nitrogen are the elements to which most attention is 

 directed. The carbon and nitrogen come exclusively from 

 the foods eaten. Much of the oxygen in the body comes 

 from the air we breathe and the water we drink. Water also 

 supplies much of the hydrogen found in the body. The other 

 elements are usually present in the food in such abundance 

 that we give very little thought to getting enough of them. 



378. Foods Must Supply the Body with Energy. The gaso- 

 line engine transforms the chemical energy (Art. 86) of the 

 gasoline into heat and power. The body likewise transforms 

 the chemical energy of foods into heat, muscular activity, 

 power to digest foods, power to think, to see, to feel, to hear; in 

 short, into all processes included in "LIFE." 



379. How the Energy of Foods is Liberated to the Body. 

 Just as the fuel for the engine" must unite with oxygen in order 

 that its energy may be delivered to the engine, so the materials 

 composing the food must undergo oxidation in the body in 

 order to liberate their energy to the body. However, in the 

 case of the fuel, the oxidation is rapid and takes place at a 

 high temperature. Such oxidation is known as COMBUSTION. 

 In the human body, oxidation is slow and proceeds at the body 

 temperature. The process is called SLOW OXIDATION. With- 

 out this slow oxidation there is no liberation of energy to the 

 body. Hence, it is evident that oxygen is just as necessary 

 as food for the maintenance of the body activities. The oxy- 

 gen comes from the air. As a result of the combination of 



