EXCRETION OF pnospnoKus 547 



of chemical analyses which indicalo the excretion of total P contained in the 

 diet of the subjects. 



From the total P of the diet excreted 33% and 35% left the body through 

 the bowels in two experiments, thus a decidedly higher figure than found for the 

 excretion of the labelled sodium phosphate. It is also higher than found in a for- 

 mer case for the amount of labelled P which left the body absorbed (13%). To 

 account for this discrepancy two different explanations can be put forward. Accord- 

 ing to one explanation, phosphorus present in some of the organic phosphorus 

 compounds of the food, is less effectively resorbed than the labelled inorganic phos- 

 phorus added to the food. Such P is only split off in the lower region of the intesti- 

 nal tract, in which place it has more chance to form insoluble calcium phosphate, 

 for example, than in the more acid tipper region. An alternative explanation is, 

 that it is not the binding of the phosphorus in the compound which matters, 

 but the mechanical protection of the phosphorus compounds present in the food. 

 From solid undigested particles, the phosphorus particles will not be leached out 

 properly. As to the resorption of phosphorus, in a recent work, carried out in 

 Verzab's laboratory, Laskowski^^^ has shown that the phosphate radical present 

 in sodium glycerophosphate, introduced artifically into the upper part of the 

 small intestine, splits off rapidly. The effect of this fast process is that the phos- 

 phate of the above mentioned compound is absorbed into the circulation as quickly 

 as that of the sodium phosphate. When experimenting on rats an absorption 

 of 68% of the P administered was ascertained, after the lapse of one hour, with 

 either compound. In the case of sodium phytin 62%, in that of sodium diphospho- 

 glycerinate only 42% of the P content was resorbed. When ths phosphorus com- 

 pounds were introduced into the lower part of the small intestine, the percentage 

 absorbed into the circulation was much smaller^^^ and amounted, in the case of 

 sodium phosphate, to 38% of that introduced. The difference observed, is pre- 

 sumably due partly to the greater activity of phosphatases in the upper part of 

 the intestinal tract, partly to the greater acidity prevailing there. We mentioned 

 already that low acidity is favourable to the formation of insoluble phosphorus 

 compounds. In so far as some of the phosphorus compounds present in the food 

 decompose or get leached out in lower parts of the intestine, the yield will be lower 

 and this may explain the difference observed between the absorption of labelled 

 sodium phosphate and the total phosphorus present in the diet of the human 

 subjects in question. We have also to consider that a part of the phosphorus may 

 be contained in undigested fractions of the diet taken, protected by mechanical 

 obstruction from the leaching effect of the digestive juices. We can expect more 

 information on these points by replacing the administration of labelled sodium 

 phosphate by that of vegetables, grown on labelled soil and thus containing labelled 

 phosphorus compounds. We can also feed labelled eggs, layed by hens to which 

 labelled sodium phosphate was administered, or labelled meat. The tracing of to 

 what extent the labelled P is absorbed from these foodstuffs is to be expected 

 to supply us with important information as to their digestibility and seems to be a 

 rational approach to the study of digestion, especially if foodstuffs containing 

 other labelled elements beside phosphorus could be administered as well. We can, 

 however, also obtain a knowledge as to the amount of unresorbed P present in 

 the faeces by an easier method than that sketched above, a method which we 

 will describe in the following. 



(i^M. Laskowsky, Biochem. Z. 292, 312, 1937. 



(2^Comp. also F. Verzar and H. Wirz, Biochem. Z. 292, 174 (1937). 



37^ 



