NUTRITION. 327 



the traces present in the food substances and also in the small amount 

 of yeast used to render the diets capable of maintaining our experi- 

 mental animals. These traces have, however, been determined by 

 chemical analyses, so that an exact knowledge of the inorganic intake 

 has been obtained. 



These studies will occupy much of our attention for some time to 

 come. One of the interesting facts thus far established is that while 

 calcium is needed in relatively large amounts, extremely small quanti- 

 ties of the other inorganic elements, with the exception of phosphorus, 

 suffice for long-continued growth. Calcium can not be replaced by mag- 

 nesium. Concerning the requirements for phosphorus, our experiments 

 are not yet sufficiently advanced to justify definite statements, since 

 the experimental conditions under which this element must be fed are 

 more comphcated than those involved in studying the other elements. 



By determining the minimum for each element and the possible 

 supplementary, or antagonistic, interrelations which they may mani- 

 fest, it ought to be possible to supplement the inorganic deficiencies of 

 certain naturally occurring foods more intelligently than can be done 

 at present. It is possible that some day more rational principles can 

 be applied to the selection of inorganic supplements to the diet, in 

 accord with the law of minimum which applies so widely in biological 

 phenomena, and that new methods may be developed for controlling 

 some of the pathological conditions with which physicians have to 

 real. A wide, new field is thus opened for future investigation of many 

 factors essential for nutrition in growth and maintenance to which 

 we expect to contribute much of interest during the coming year. 



Stimulated by the desirability of obtaining other sources of water- 

 soluble ^dtamine which might enable us to improve our methods for 

 studying many problems of nutrition and metabolism which otherwise 

 would be impossible, we are investigating many naturally occurring 

 substances. In view of the marked superiority of our ''protein-free 

 milk," both as a source of water-soluble vitamine and suitable inor- 

 ganic salts, we have tested by-products of the milk industry, hoping 

 that these might afford a cheap and easily obtainable substitute for 

 the product which we have heretofore made in our laboratory. The 

 outcome has been disappointing, probably omng to the commercial 

 methods used in handling the milk-sugar residue. 



A number of our former experimental animals showed in their 

 kidneys or bladder the presence of phosphatic calcuU. Since none of 

 our stock animals was ever thus afi'ected, it was of interest to correlate 

 this condition with the diet used. Of the 81 rats which developed 

 calculi, out of 857 rats autopsied, 79 had been deprived of the fat- 

 soluble vitamine for periods of from 35 to 325 days. One of the 

 remaining two was without this substance for 21 days and the other 

 for 11 days. The latter was a very young rat from a lot of physically 



