FORBES! MINERAL ELEMENTS IN NUTRITION 441 



ganic phosphorus may be had in unlimited quantities as pre- 

 pared from old bones and rock phosphate, and the inorganic 

 phosphorus content of foods may be greatly increased by the 

 fertilization of the soils upon which they are grown. Organic 

 phosphorus we get from such expensive foods as milk, eggs, and 

 beef, and from cereals. The organic phosphorus content of 

 foods is not susceptible of important modification by treatment 

 of the soil. 



In this study we included orthophosphates because of their 

 cheapness and availability, hypophosphites because they are 

 so much used in human medicine, phytin as an especially abund- 

 ant phosphorus storage compound of vegetable foods, glycero- 

 phosphates because of their relation to lecithin, a universal cell 

 constituent, and nucleic acid because it is found in the nuclei of 

 all cells. 



These compounds in the pure form were added to a low- 

 phosphorus basal ration in amounts contributing equal quanti- 

 ties of phosphorus. The subjects were growing pigs. Results 

 were obtained by the method of the metabolism experiment 

 and by the analysis of the carcasses of the animals. 



It would seem, at first glance, that this problem should readily 

 yield to careful experimental investigation, but intimate ac- 

 quaintance has shown it to be extremely complicated and dif- 

 ficult. Many investigators have studied it, and the problem 

 has been finally answered many times but in many different 

 ways. If this problem is settled, in the end, as many such 

 subjects of controversy have been, most of those who have 

 studied it will be at first surprised, then chagrined, and then 

 gratified that so much of truth was found on both sides of the 

 discussion. Recent evidence has been mostly with those who 

 believe that inorganic phosphorus can serve all of the purposes 

 for which animals need phosphorus, but there is still much un- 

 controverted evidence that there are differences in the metabo- 

 lism of some organic and inorganic phosphoric compounds which 

 imply at least a greater usefulness of some organic compounds 

 for some purposes with some animals. 



