442 FORBES! MINERAL ELEMENTS IN NUTRITION 



In our work orthophosphates, glycerophosphates, hypophos- 

 phites and yeast nucleic acid, when added in the pure form to 

 rations which are low in phosphorus but capable of maintaining 

 phosphorus equilibrium, were all to some extent absorbed and 

 retained. 



Prominent differences were observed in the tolerance of the 

 pigs for these pure phosphorus compounds. The limit of toler- 

 ance for glycerophosphates was not reached in any of our tests, 

 but the other compounds were not so well taken. These drugs, 

 when taken into the alimentary tract in quantity, in readily 

 soluble condition, produced marked specific therapeutic effects 

 which were, at least to a large extent, unrelated to fundamental 

 nutritive values, and were likewise different from the effects of 

 the same compounds as occurring in their natural physical and 

 chemical relationships in foods. It is, therefore, impossible 

 to state, from investigations of this sort, on pure compounds, 

 what may be their nutritive values in common foods. 



That the particular organic compounds used in this investi- 

 gation (nucleic acid, phytin, and glycerophosphates) have 

 nutritive values, to growing swine, superior to simple inorganic 

 phosphates was not shown. No fundamental differences in 

 the methods of usefulness of the phosphorus compounds studied 

 were established, though, under our experimental conditions, 

 they differed greatly in the extent of their usefulness; for in- 

 stance, glycerophosphates were acceptable and useful in large 

 quantities, the limit of which was not reached in our work; 

 orthophosphates were distinctly less acceptable; phytin and 

 nucleic acid were tolerated in still smaller amounts; while hypo- 

 phosphites were the least acceptable of all. Still, so far as our 

 results indicate, these compounds were all useful in the same way. 



No basis was discovered for a differentiation between the 

 nutritive values of organic and inorganic phosphorus compounds 

 generally. It should be borne in mind, however, that no repre- 

 sentatives of the two classes, phosphoproteins and lecithins, 

 were included in this investigation, and results obtained under 

 conditions of such rigid experimental control may not accurately 

 represent the facts under optimum, normal conditions of life. 



