FOODS 65 



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 various ingre- 

 dients of the food, liquefying them and rendering them capable 

 of absorption. 



II. The mineral salts which are chiefly necessary for nutrition 

 are: 



Of sodium and potassium. 



Chlorides 

 Phosphates 

 Sulphates 

 Carbonates 



Phosphates j . 



> Of calcium and magnesium. 

 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, especially the blood. 

 Of the other salts, those of calcium exist in the largest quantity 

 in the body. They are especially important 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 and 

 sugars. They are of definite chemical composition containing 

 carbon, hydrogen and oxygen, but no nitrogen. The hydrogen 

 and oxygen which they contain are always in the proportion to 

 form water, i. e., two atoms of hydrogen to one of oxygen. The 

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