IN RELATION TO THE WAR. 497 



to the problem of the amount of protein actually needed for normal 

 human nutrition have recently been discussed elsewhere.^ The 

 average of the " requirements " indicated in the 86 experiments 

 which seemed to be applicable under the necessarily somewhat arbi- 

 trary criteria adopted for the sake of minimizing the personal equa- 

 tion in selection and interpretation of results, was 49.2 grams (or 

 say 50 grams) per man per day, which agrees almost exactly with 

 Chittenden's estimate based chiefly upon the results of his own ex- 

 periments. Thus the net result of all subsequent work up to date 

 does not differ materially from Chittenden's findings of a decade 

 ago. This may be accepted as the best evidence yet available re- 

 garding the amount of protein actually required in normal human 

 nutrition without entering upon any discussion of the question as to 

 how much more than this it is desirable to consume. In other 

 words in speaking of the requirement we imply nothing as to the 

 best dietary standard for protein. 



As compared with this actual requirement of not over 50 grams, 

 the average amount of protein in typical American dietaries, as 

 judged from the 250 studies of families or larger groups the data 

 of whose food consumption has been most fully worked out, is 106 

 grams per man per day. The average of typical American dietaries 

 thus shows in its protein content a margin of safety of 112 per cent. 



Of the inorganic elements essential to nutrition, most are be- 

 lieved to be furnished in abundance by the ordinary American food 

 supply with the table salt commonly added to it, but recent research 

 has shown that three of these elements cannot properly be dismissed 

 with this assumption. These are phosphorus, calcium, and iron. 



It is sometimes stated that our knowledge of the amounts of 

 these elements required in nutrition is so meager as to make the 

 interpretation of dietary data more difficult here than in the case of 

 protein. Until recently this was true of all three of these elements 

 and it is still true of iron ; but the quantitative metabolism of phos- 

 phorus and calcium has lately been investigated with sufficient thor- 

 oughness so that we now know the normal nutritive requirement 

 for these elements with about the same degree of accuracy as we 

 know the protein requirement and can estimate the margin of safety 



2 Lecture before the Harvey Society, New York, Jan. 12, 1918. 



