FOODS 135 



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, e.g., 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. 



Independent of the foregoing facts it has also been determined that 

 animal proteins and vegetable proteins do not possess the same value for 

 promoting growth and repair of tissues or in their capacity to restore the 

 daily protein loss for the following reasons. It has been stated on a 

 previous page that proteins in general consist of simple chemical units 

 termed amino-acids. The actual number as well as the percentage of the 

 units vary in the different proteins. This fact determines their nutritive 

 value. A simple protein that would provide the requisite number and the 

 necessary percentage of amino-acids required for growth and repair, 

 whatever its source would be sufficient for both purposes if consumed 

 in proper quantity. Proteins of this character are found in milk, eggs 

 and meats. The proteins of these foods, viz., casein, albumin and vitellin 

 and myosinogen furnish all the amino-acids necessary for growth and 

 tissue repair. 



The vegetable proteins as a class do not possess an equal value in this 

 respect and in individual instances have a different physiologic action. 

 Thus the protein of wheat consists of two forms, viz., glutinin and gliadin 

 both present in about equal proportions. Glutinin in sufficient amount 

 promotes growth and maintains body weight in a manner closely resembling 

 casein when the usual quantities of fat and carbohydrate are given with it. 

 The supposition is, therefore, that it contains all the amino-acids necessary 

 for nutritive purposes. Gliadin, however, when given in combination 

 with fat and carbohydrates, is incapable of promoting growth and the 

 animal remains undersized. One reason assigned for this is the absence 

 from gliadin of an important amino-acid, lysin. What is true of gliadin 

 is true of one of the proteins of corn, viz., zein, which is lacking in trypto- 

 phan. It has been found by direct experiment that in order to protect the 

 body from protein loss, twice as much bread protein, and three times as 

 much corn protein as meat or milk protein are required (Lusk). 



