258 SCIENCE REMAKING THE WORLD 



efficiency shown by certain individual proteins taken 

 singly do not imply any great danger that the daily food 

 will furnish inefficient protein, because the articles of 

 food which we actually use contain many kinds of pro- 

 tein and these different proteins supplement each other. 

 To explain this fully would require too long a discussion 

 of the individual amino acids of which the proteins are 

 composed. 



THE MINERAL ELEMENTS AND VITAMINS OF FOODS. 

 Besides the five chemical elements of which simple pn> 

 teins are composed, about a dozen more are now known 

 to be essential to human nutrition; and besides the 

 chemically known organic foodstuffs at least three other 

 organic substances, vitamins A, B, and C, are also nec- 

 essary. Space does not permit the discussion here of 

 even the more important of our recent advances in the 

 study of the mineral elements of food, and the vitamins 

 need not be further discussed in this chapter since they 

 are treated elsewhere in this volume by Doctor Eddy. 

 It must, however, be emphasized that the recently 

 developed knowledge of the nutritive importance of 

 the mineral elements and vitamins and of the very un- 

 even distribution of these dietary essentials among the 

 different articles and types of foods has greatly clarified 

 our ideas of food values. For progress in this line of 

 study we are greatly indebted to McCollum and Sim- 

 monds, formerly of the University of Wisconsin and 

 now of the Johns Hopkins University. It was for- 

 merly customary to speak as though dietaries could be 

 "balanced" by a consideration of protein, fat, and car- 

 bohydrate, whereas we now see clearly that the mineral 



