STUDIES OX THE METAHOLISM OF PHOSPHOKVS IX AXIMAT.S 157 



of phosphorus in organic form. Although the ]a11(M' does not exchange 

 ^vith the atoms of the inorganic radioactive phosphate, the l)ulk of the 

 j)hosphorus (0.0795 per cent) reaches a state of kinetic equiUbrium 

 with the radioactive phosphate added and l)ecomes radioactively indi- 

 cated. During the digestion process the 0.036 per cent will be set free 

 from its molecular binding and only at this stage will it have an oppor- 

 tunity to become thoroughly mixed (in an atomic sense) with the radio- 

 active phosphate atoms. While, as has already been mentioned, it would 

 be preferable in investigating phosphorus metaboHsm to utilize food 

 in which all the phosphorus atoms are labelled, it is not probable that 

 the information obtained with such material would be appreciably 

 different from that obtained in the experiments described in this paper. 

 Experience shows that the retention of phosphorus docs not depend 

 on the form in which the phosphorus is present^ in the food, on whether 

 it is present as inorganic and thus exchangeable phosphate or as non- 

 exchangeable. Ducks reared on diets containing phosphate only in inor- 

 ganic form matured normally and laid 85 to 795 eggs during the first 

 summer^. About 15 per cent of the phosphorus present in nu^at. more 

 than half that present in milk, and the greater part of that present in 

 vegetables, i.e. the bulk of the phosphorus eaten, is present in inorganic 

 and thus exchangeable form. 



Rats are inclined to eat their offspring and they could easily be fed 

 on young rats born by a mother fed on radioactive phosphorus, but 

 the chief source of phosphorus would in this case, too, be inorgani(; 

 phosphorus, namely that present in the skeleton. 



ELIMINATION OF PHOSPHORUS BY RATS 



We carried out numerous experiments with rats which were fed on a 

 normal diet to which radioactive phosphorus was added. In some cases 

 we added 0.1 mgm or less in the form of sodium phosphate dissolved 

 in a few drops of water which was then soakerl up by a small piece of 

 bread given to the animal. The average of several experiments gave a 

 total excretion of 26 per cent through the kidneys and of 32 per cent 

 through the gut. In some other experiments calcium ]>hosphate was 

 administered, mixed with butter, which was given to the rat on a small 

 piece of white bread. The result of such an experiment is seen in Table 3. 

 which contains the results of the analysis of the urine and the faeces 

 collected during 19 days. The urine was concentrated by evaporation, 

 ti'eated with fuming nitric acid, and ignited; a known frac-tion of the ash 



iM.,Spkir8 and H. C. Sherman, J. Nutrit. 11, 2ir) (1036). 

 -G. FiNGERLiNG, Biochem. Z. 38, 44<S (101 1). 



