McCOLLUM— RELATION OF DIET TO PELLAGRA. 43 



quantitative comparison of the protein mixtures derived from pairs 

 of seeds in considerable number. 



Mixtures of seeds, or of seeds, tubers, and roots, will in all cases 

 require supplementing with respect to calcium, sodium, and chlorine 

 among the inorganic elements, and fat-soluble A. In most such 

 mixtures the quality of the proteins will likewise be sufficiently poor 

 to require improvement before the optimum well-being can be 

 secured. 



We are now in possession of a considerable amount of knowl- 

 edge concerning the distribution of the dietary factor, fat-soluble A, 

 in animal tissues. The body fats of the ruminants will probably 

 always be found to be richer in this substance than the body fats of 

 the omnivora because of the greater intake of it in the food. Mus- 

 cle tissue has been found to be very poor in fat-soluble A, but the 

 fats from the glandular organs, i. e., intracellular fats, are a good 

 source of it. It follows, therefore, that muscle tissue such as round 

 steak should not supplement mixtures of vegetable foods which be- 

 long to the storage organ group with respect to fat-soluble A, and 

 in our experience this proves to be the case. The inorganic content 

 of muscle tissue resembles in a general way that of the storage or- 

 gans of plants except in its very low content of magnesium. It is 

 too poor in calcium, and to a lesser degree in sodium and chlorine, 

 to support the optimum well-being in an animal. Muscle tissue 

 fails to supplement the seeds, tubers, and roots on the inorganic side. 

 The protein content of muscle tissue is high and the proteins are 

 probably of high biological value, and, except as respects palata- 

 bility, it is only in improving the quality of the protein content of 

 the ration that the addition of meats of this class enhances the value 

 of a mixture of products derived from the storage organ group of 

 plant products. 



These considerations indicate the basis for our distinction be- 

 tween two groups of foodstuffs. One of these, which includes 

 milk, eggs, and the leafy vegetables, we have designated as "pro- 

 tective foods," in order to call attention to their special importance 

 in the diet. They are protective in that they are so constituted with 

 respect to their inorganic content, content of fat-soluble A, and the 

 quality of their proteins that they correct in great measure when 



