FOODS 



of the cellulose envelope, especially in ripe beans and peas, combined with 

 rather a dense texture, renders them somewhat difficult of digestion. Pota- 

 toes, though largely employed as food, are extremely poor in protein, 2 per 

 cent., and carbohydrates, 20 per cent. When sufficiently cooked they are 

 easily digested, owing to the small amount of cellulose they contain. 



Green vegetables, e.g., lettuce, spinach, tomatoes, asparagus, onions, 

 etc., though containing food principles in small amounts, are, nevertheless, 

 valuable adjuncts to the dietary, for the reason that they contain inorganic 

 as well as organic salts, which appear to be necessary to the maintenance 

 of the normal nutrition. The want of green vegetables has been supposed 

 to be the cause of scurvy. 



Ripe fruits, grapes, cherries, apples, pears, peaches, strawberries, lemons, 

 oranges, etc., though consumed largely, possess but little nutritive value. 

 They consist largely of water, 75 to 85 per cent., proteins a trace, sugar 

 from 5 to 13 per cent., organic acids (citric, malic, tartaric), pectose, and 

 various inorganic salts. 



Relative Value of Animal and Vegetable Foods. Though both 

 animal and vegetable foods contain the different classes of food principles, 

 it is not a matter of entire indifference as to which are consumed. It has 

 been found by experiment that animal proteins are more easily and com- 

 pletely digested and absorbed than vegetable proteins; that cellulose is not 

 only highly indigestible, but by its presence in large quantities retards the 

 digestive process and impairs the activity of the entire digestive mechanism, 

 though in moderate quantity it undoubtedly aids digestion indirectly by 

 mechanically promoting peristalsis. The following table shows the relative 

 digestibility and availibility of the two classes of foods: 



