BIOLOGICAL CLASSIFICATION OF FOODS 51 



purified protein (casein), milk-sugar (supposedly pure), salts in 

 imitation of the mineral matter of milk, and milk-fat. They 

 could see no reason why the polished rice, supplemented by puri- 

 fied protein, suitable salts and milk-fat should not be a complete 

 food. This was cleared up subsequently by establishing the 

 fact that the milk-sugar used in the former of these two experi- 

 ments, and the germ or chit of the cereal seeds, which had been 

 rubbed off the rice, contain a water-soluble substance essential for 

 growth, health and vigor. 



The conclusions finally reached were, first, that amongst 

 the food substances (protein, carbohydrates and ash or mineral 

 matter) coming from different sources there is a marked differ- 

 ence in quality, and that those from milk are of a very high order; 

 and second, that there are two as yet unidentified substances 

 which are indispensable to growth and health, namely, the 

 unknown substance which is present in milk-fat, the fat of yolk of 

 egg and some of the glandular fats, which McCollum and Ken- 

 nedy subsequently designated " fat-soluble A," and a second 

 substance soluble in water, which they designated " water- 

 soluble B." The absence of the former (fat-soluble A) not only 

 prevents growth, but also causes a serious eye trouble which, if 

 not corrected in time, will end in blindness and death. We have 

 already illustrated this point. The absence of the water- 

 soluble also prevents growth, and causes serious physiological 

 disturbances resulting in a form of paralysis, beri-beri, which is 

 quite prevalent where such foods as polished rice and bolted 

 flour form the main article of diet. 



But this water-soluble is present in most ordinary food 

 substances, and particularly in a mixed diet, whereas the sources 

 of the fat-soluble are quite limited, the fat of milk, in the form 

 of milk and butter, being the chief of these. 



In support of what has been said, the utterances of some of 

 our leading physiologists and students of nutrition may be 

 quoted. 



Dr. H. C. Sherman, Professor of Food Chemistry, Columbia 

 University: " Especially in the feeding of children should milk 

 be used freely, because of its many advantages as a tissue- 



