MINERAL METABOLISM 325 



The inquiry into P metabolism is still centered about the question of 

 the availability of inorganic forms of P for the animal organism. De- 

 terminations of the P and N exchange usually indicate better retention 

 when the P is supplied in organic combination (Masslow(a) ; LeClerc and 

 Cook; Hirschler and Terray) and this is likewise the case for Ca retention, 

 but in work on cows it has recently been shown that if the ingestion of a 

 Ca rich food, as hay, is alternated daily with the ingestion of a food low in 

 Ca and to which inorganic phosphates have been added, there is good 

 retention of both P and Ca (Meigs, Blatherwick and Cary). Berg in a 

 metabolism experiment on himself could show no P retention on addition 

 of Ca(H 2 PO 4 ) 2 or Ca(H 2 PO 2 ) 2 to a diet supplying 3.04 g. HPO 4 daily. 

 On the other hand Forbes (6) in experiments on swine finds orthophos- 

 phates and hypophosphites as satisfactory forms in which to supply P as 

 are nucleic acid, phytin or glycerophosphates. Fingorling found the same 

 for ruminants and ducks. Osborne and Mendel were able to supply prac- 

 tically all of the mineral constituents in the form of inorganic compounds 

 and still get normal growth in rats. Experimental work is somewhat incon- 

 clusive because the effort to prepare a diet supplying enough protein and 

 energy with a minimum of P in organic combination may result in an 

 insufficient supply of the animo acids or of the food accessories (vitamins) 

 and nutritive failure follows irrespective of the form of P. That inor- 

 ganic phosphates are utilized to a degree is unquestionably established, but 

 there is still a lack of quantitative work which would establish the percent- 

 age of absorption from each source. That this is different seems clear from 

 the fact that the percentage of the ingested P retained by infants is higher 

 when they are breast-fed (human milk contains about 77 per cent of its 

 P in organic combination) than when fed on cows' milk which contains 

 about 27.9 per cent of its P organically combined (Keller; Schlossmann). 

 Marshall in a review of the subject concludes that inorganic forms are as 

 satisfactory as organic, but others, notably Sherman and Forbes, take the 

 more conservative view and (are willing to) grant an advantage, though 

 possibly not indispensability, to the organic forms. 



Of the mineral constituents of the body P is the most universally re- 

 quired, by bone, muscle, gland and nerve; P retention is the rule and 

 in this respect and because its retention is frequently independent of the 

 N" balance, Albu-Neuberg compare P with fat. In infants P retention is 

 0.02-0.03 g. P 2 O 5 per kg. body weight per day, in growing children 

 it is 0.027-0.042 g. per kg. (Herbst(a)(6)), in adolescent boys it is 

 0.004-0.015 and may be said to be independent of the N balance, al- 

 though the lowest P retention found, 0.04 g. P 2 O 5 per kg., accompanied a 

 negative N balance. The retention of P 2 O 5 was twice as great as would 

 have been required by the retained N and Ca for building bone and muscle. 

 Cronheim and Miiller(6) found a similar retention of P in excess of the 

 amount required by the retained Ca and N and conclude "P rich nerves 



