Chap. XIV.] ALIMENTATION. 171 



The carbo-hydrates contain in every 100 parts about : — 



Carbon 44 parts 



Hydrogen 6 " 



Oxygen 50 " 



The principal carbo-hydrates are starch and sugars. Starch is 

 found in wheat, Indian corn, oats, and all grains, in potatoes, 

 peas, beans, roots and stems of many plants, and in some fruits. 

 In a pure state, it appears as a white powder, as in arrowroot 

 and cornstarch. Under the influence of dry heat, starch may 

 be converted into a soluble substance, called dextrine; and, 

 under the action of certain of the digestive juices, at the tem- 

 perature of the body, into sugar. Of sugars there are several 

 kinds : cane sugar or sucrose, obtained chiefly from the sugar- 

 cane, beet sugar, and maple sugar ; grape sugar or glucose, found 

 in grapes, peaches, and other fruits (it is also readily manufac- 

 tured from starch); rtialt sugar or maltose, obtained from malt; 

 milk sugar or lactose, obtained from milk. 



Carbo-hydrates are readily oxidized ; together with fats, they 

 are often classed as " non-nitrogenous " food-stuffs. 



Water is a compound of oxygen and hydrogen, water being 

 produced whenever two molecules of hydrogen unite with one 

 of oxygen. Next to air, water is the most necessary principle 

 of life. It forms about seventy per cent of the entire bodily 

 weight. It is an essential constituent of all tlie tissues, as 

 well as forming the chief part of all the fluids of the body. 

 It acts as a solvent upon various ingredients of the food, lique- 

 fying them and rendering them capable of absorption. Most 

 of the water of the body is taken into it from without, but it 

 is also formed within the body by the union of hydrogen and 

 oxygen in the tissues. 



Mineral salts. — The mineral substances chiefly necessary for 

 nutrition are : — 



Chloride 

 Phosphate 

 Sulphate 

 Carbonate J 



- of soda and potash. 



Phosphate! „ ,. , 



^ , ^ 01 lime and magnesia. 



Carbonate J 



