FOODS AND THEIR USES 45 



we burn bones, about one third of the weight disappears, the 

 remaining two thirds being bone ash, which is the mineral 

 matter. Every part of the body, however, contains some 

 mineral ingredients ; for when muscle, liver, brain, or blood 

 is burned, there remain some traces of ash in each case. 



46. Water. The great importance of water in the com- 

 position of the human body is evident from the fact that this 

 compound forms about 62 per cent of the weight of an adult. 

 Hence, if all the water were removed from the body of a man 

 weighing one hundred and fifty pounds, the solids that re- 

 mained would weigh less than sixty pounds. The different 

 organs vary greatly in their percentages of water; bones 

 contain about 22 per cent, muscles have 75 per cent, and the 

 kidneys 82 per cent. 



II. THE NECESSITY FOK FOODS 



47. Necessity of foods for growth. During the earlier 

 years of life, as we all know, the human body rapidly increases 

 in weight. A child at birth usually weighs seven to eight 

 pounds, whereas the weight of a fully grown man is often 

 one hundred and fifty pounds or more. Hence during a 

 lifetime there is often a twentyfold increase in weight. To 

 provide for this increase or growth a large amount of new 

 material must of course be taken in by the human being, 

 and this material is supplied by the food. 



48. Necessity of foods for repair and for the production 

 of energy. On the other hand, it is not difficult to prove 

 that throughout life the body tends constantly to decrease 

 in weight. For instance, if one were weighed on accurate 

 scales immediately after eating and then again after several 

 hours had elapsed and before food or drink had been taken, 

 a decrease in weight would .be noted. Still more striking is 



