NUTRITIONAL REQUIREMENTS — ELVEHJEM 297 



tlie ruminant can get along on diets practically devoid of the vita- 

 min B complex because all these factors are synthesized by the bac- 

 teria in the rumen. Recent work indicates that the rat can syn- 

 thesize some of the unknown members of the B complex and that 

 high levels of pantothenic acid apparently favor this synthesis. 



If we turn to the guinea pig we find quite different results than 

 those obtained with other animals. A young guinea pig fails to grow 

 normally and dies in a few weeks when fed purified diets upon which 

 rats and dogs may grow very well. We have found that these animals 

 will grow if we supplement the purified diet with dried grass, yeast, 

 and fresh milk. Chicks also require additional amino acids and cer- 

 tain factors from yeast before they will develop normally on synthetic 

 diets. How these facts relate to human nutrition is not known, but 

 these results do suggest the importance of additional work. These 

 problems require all the ingenuity that chemists can contribute. 



In conclusion then, we may agree that the nutritional requirements 

 of man can be expressed in quantitative terms to a very extensive de- 

 gree. These values are of great importance in constructing adequate 

 diets provided we still obtain a considerable proportion of the nutrient 

 from natural foods. The safest program for the future involves the 

 improvement of natural and processed foods through restoration and 

 fortification. Thus recent criticisms leveled at the fortification pro- 

 gram are invalid because we are not adding enriched foods to synthetic 

 diets but to diets that are already fairly adequate. The fortification 

 of foods like bread merely brings the diet from a boi-derline state of 

 adequacy to an optimum and efficient state. We may not have all the 

 knowledge for optimum fortification but as long as the use of natural 

 foods is continued, the danger of imbalance is greatl}' reduced. 



REFERENCES 



1. Mills, A. A., and Calvin, J. W. 



1940. Vitamin Bi. Science, vol. 92, No. 2394, Snppl., p. 9, Nov. 15. 



2. Bbown, R. B., Hansen, A. E., Bx;bb, G. O., and McQuarrie, I. 



1938. Effects of prolonged use of extremely low-fat diet on an adult 

 human subject. Journ. Nutr., vol. 16, No. 6, pp. 511-r>24. 



3. Van DmNE, F. O., Lanfokd, O. S., Toepfeb, E. W., and Sheeman, H. C. 



1941. Life-time experiments upon the problem of optimal calcium intake. 



Journ. Nutr., vol. 21, No. 3, pp. 221-224. 



4. Kbieger, C. H., Bunkfeldt, R., Thompson, C. R., and Steenhock. H. 



1941. Cereals and rickets. XIII. Phytic acid, yeast nucleic acid, soy- 

 bean phosphatides and ignorganic salts as sources of phosphorus 

 for bone calcification. Journ. Nutr., vol. 21, No. 3, pp. 213-220. 



5. Tompsett, S. L. 



1940. The iron of the plasma. Biochem. Journ., vol. 34, No. 6, pp. 

 959-960. 



