

SECTION IX 

 THE FOOD AND DIGESTION 



I. FOOD 



The great use of food is to supply energy to the body. The 

 muscles of the body are constantly active; they are con- 

 stantly liberating energy by breaking down the complex 

 molecules of proteids, fats, and carbohydrates, and hence a 

 constant fresh supply of such material is necessary to pre- 

 vent the body living on its own material and wasting away 

 (see p. 73). During the growth of the body, too, the material 

 from which it is to be built up, and the energy used in its 

 construction, must be supplied by the food. 



Hence a suitable food is one which will yield the necessary 

 amount of energy, and will supply the materials necessary 

 for repair and for growth. 



But food must also supply the water and salts required to 

 keep the various constituents of the body in solution, so that 

 the essential chemical changes may go on. 



Nature of Food. 



Food may be divided into foods not yielding energy and 

 foods yielding energy the former acting chiefly as solvents. 



A. Food-stuffs not yielding Energy. 1. Water is the 

 chief constituent. Since it is daily given off in large 

 quantities by the kidneys, lungs, skin, and bowels, it must 

 daily be supplied in sufficient amounts or the chemical 

 changes cannot go on and death supervenes. 



2. Inorganic salts. The most important of these is 

 chloride of sodium, which is essential for the maintenance of 

 the chemical changes in the body. When it is not freely 



