FOODS 65 



stances are taken into the alimentary canal as food ; but ex- 

 amination reveals that all such materials contain one or more 

 of a very few classes of food stuffs. These may be divided 

 as follows: 



I. Water. 

 II. Inorganic or mineral salts. 



III. Carbohydrates. 



IV. Fats. 



V. Proteids. 



I. Water is scarcely looked upon as food in the common 

 acceptation of the term, but it is quite as necessary to cell life 

 as any of the other classes. It is found in all foods and in 

 all tissues and fluids of the body. It forms about 70 per cent, 

 of the entire body weight and acts as a solvent upon vari- 

 ous ingredients of the food, liquefying them and rendering 

 them capable of absorption. 



II. The mineral salts which are chiefly necessary for nutri- 

 tion are: 



Chlorides "1 



Sujhater f Of sodium and P tassium - 



Carbonates 



Phosphates V Qf ca]cium and esium 



Carbonates J 



Of these salts, sodium chloride, or common table-salt, is the 

 most important and abundant in the foods we eat. It is 

 present in nearly all the tissues and fluids of the body, es- 

 pecially the blood. Of the other salts, those of calcium exist 

 in the largest quantity in the body. They are especially im- 

 portant on account of the part they play in the formation of 

 the bones, teeth and cartilages. The remaining salts exist 

 in larger or smaller quantities in the tissues and fluids of the 

 body. 



III. The carbohydrates include principally the starches 



