BIOLOGY IN HUMAN AFFAIRS 



the nature and extent of the deficiencies of the different 

 natural foods. On the basis of such data it is possible to 

 theorize concerning which natural foods, individually- 

 lacking or deficient in one or another food principle, 

 should, when combined, supplement each other's de- 

 ficiencies. Experimental verification of predicted results 

 confirms in a highly satisfactory manner the belief that we 

 understand, to a great extent, the nutritive needs of the 

 body and the dietary properties of most of our natural and 

 manufactured foods. 



Since most foods have been shown to be deficient or 

 lacking in one or more of the nutrient principles, it is 

 necessary for us to combine foods of unlike composition 

 so that one will provide what the other lacks. Herein 

 lies the cause of safety in variety in eating. The whole 

 wheat kernel, which many people have long believed to 

 be a complete food, is incapable, when fed as the sole 

 source of nutriment, of supporting growth of the young or 

 prolonged health in the adult. It is deficient in three 

 respects : (1) it lacks sufficient calcium; (2) it lacks sufficient 

 vitamin A; and (3) its proteins require supplementing with 

 proteins from other sources which supply in abund*ance 

 certain amino-acids which the wheat proteins contain in 

 amounts too small to serve as building stones when food 

 proteins are converted into body proteins. Even though 

 wheat is supplemented with one or two of these substances 

 in which it is deficient, the nutrition of an animal will 

 not be so good as it will if all three are added to the diet. 



The Vitamins. There are three vitamins — A, D, and E — 

 which dissolve readily in fats and are found only in certain 

 fats which our foods contain. They do not, in general, 

 occur together. Vitamin A is abundant in cod liver oil, 

 butter fat, and milk fat; in the glandular organs of ani- 

 mals, such as the liver, kidney, sweetbread, etc.; and in 

 all yellow pigmented vegetables. It never occurs in 



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