440 FORBES: MINERAL ELEMENTS IN NUTRITION 



proportions in the food, and we did not find the calcium reten- 

 tion to be limited by an excess of magnesium in the food except 

 perhaps in one ration, composed of rice polish and wheat bran 

 and containing 12 times as much magnesium as calcium. In this 

 case the great excess of magnesium seems to have been unfavor- 

 able to calcium retention. This proportion seems not to be a 

 matter of practical importance in ordinary rations. 



The phosphorus balances in these rations were always posi- 

 tive, but the retention was much below normal on the ration of 

 corn alone. The more important reason for this deficient stor- 

 age of phosphorus from corn was the lack of calcium, since 

 calcium was more deficient than phosphorus, and since neither 

 can be stored in large quantity except as they are combined in 

 the calcium phosphate of the bones. 



There were large excesses of inorganic acid elements in these 

 rations. They were neutralized by ammonia. We observed 

 no evidence of acid intoxication. We do not have knowledge 

 of any such prevalence of acid intoxication in domestic animals 

 as that with which we are familiar in human beings. 



The urinary ammonia excretion was found to vary in the 

 same order with the excess acid of the ration, providing that the 

 protein remained about the same in amount; but any consider- 

 able increase in the food protein also increased the urinary 

 ammonia. 



Another series of experiments with swine dealt with phos- 

 phorus metabolism. Considering the phosphorus compounds 

 of plants and animals the most obvious distinction among the 

 various groups is that in certain of these the phosphorus is 

 organically combined, as part of the living tissue, while in others 

 it is present as simple salts of the mineral bases, either in solu- 

 tion, or deposited in supporting structures (in animals), or as 

 crystals or incrustations (in plants). Our object was to learn 

 whether organic and inorganic phosphorus in the food could 

 serve equally well all of the purposes for which the animal needs 

 phosphorus. 



Our practical interest in the problem is due largely to the 

 relative availability of organic and inorganic phosphorus. Inor- 



