McCOLLUM— RELATION OF DIET TO PELLAGRA. 45 



nounced that we are of the opinion that even in those human die- 

 taries in which such calcium-rich food as milk is used in fair liber- 

 ality, the intake of calcium may be still below the optimum, and that 

 a direct addition of this element in the form of the carbonate or 

 lactate might be of distinct benefit in human nutrition except per- 

 haps in those regions where the w-ater is unusually rich in calcium 

 salts. Since civilized man usually adds sodium chloride to his foods 

 to suit the taste, the shortage of sodium and chlorine in the diet of 

 man presents no problem. An addition of calcium could be most 

 conveniently made to our foods through the use of a mixture of 

 equal parts of common salt and of calcium carbonate in the kitchen 

 and on the table. 



A question \\hicli has never been answered to the satisfaction of 

 physiologists is : How nuich protein should the diet contain in order 

 to maintain physiological well being? At about the time when the 

 question was being most discussed, the chemistry of the proteins 

 was developed to a point which made it clear that there were great 

 differences in the biological values of the proteins from dift'erent 

 sources, depending on their yields of certain amino-acids. This 

 makes futile any attempt to establish a particular intake of protein 

 which may represent the minimum, optimum, or maximum amount 

 consistent with maintenance of " normal " vitality and health. The 

 quality of the proteins must be known before anything can be said 

 about the amount of protein necessary. From biological tests we 

 now know that the proteins of the pea or navy bean are worth only 

 about half as much for growth in the rat as are equal amounts of 

 proteins from one of the cereal grains, and that the latter have about 

 half the value for the conversion into body proteins which can be 

 shown for the proteins of milk. The relative values of the proteins 

 from different sources, as well as the absolute values of certain of 

 them, are just now becoming appreciated. 



There are two opposing views regarding the amount of protein 

 which will produce the best results. Those who advocate the low 

 protein diet point to the "specific dynamic action" of protein, 

 through which it stimulates metabolism. They believe that a high 

 consumption of protein furnishes pabulum for the development of 

 an excessive growth of putrefactive bacteria, with the result that 



