550 ADVENTURES IN RADIOISOTOPE RESEARCH 



excreted P, we can conclude that, from the total food P taken by the rat, 33% 

 was unabsorbed^i^ The daily diet of the rat contained about 30 mgm P. 



Similar values for the ratio of the specific activity of the urine P and faeces 

 P were obtained in experiments with other rats kept on the same diet. The values 

 obtained were 2.29, 2.47, 2.61, and 3.10 respectively. The samples were collected 

 30, 98, 10 and 20 days respectively after the administration of labelled sodium 

 phosphate. 



Table 10. — Specific Activity or Urine P and 

 Faeces P of a Rat 98 Days after Administration 

 OF Labelled Sodium Phosphate by Subcutan- 

 eous Injection. Weight of Rat 208 gm 



It is interesting to compare the figures with those obtained when labelled sodium 

 phosphate is administeied to the rat by mouth, the animal killed, and the activity 

 of the total intestinal tract investigated after the lapse of 4 hours. Such deter- 

 minations were carried out by several investigators. We found^^% 4 hours after 

 administering labelled sodium phosphate (having a P content of about 1 mgm) 

 to a fasting rat, that the total digestive tract and its content contained 12.7% 

 of the phosphate administered; thus more than 87.3% was absorbed. The latter 

 figure represents the lower limit, since some of the active P present was actually 

 absorbed and got subsequently with the digestive juices into the intestinal tract 

 again and some active P present in the food exchanged with the tissue phosphate 

 of the intestinal tract before the active P had an opportunity to be absorbed. 

 Still higher figures for the labelled P absorbed into the circulation are recorded 

 by Artom, SARZANAand Segre,^^^ namely 88—97.9%; the duration of their experi- 

 ments was appreciably longer, it varied from 9 hours to 4 days. A smaller absorp- 

 tion was found by Dols and Jansen^*^; after the lapse of 8 hours, the stomach and 

 small intestine alone are stated by them to have contained 4.1—15.4% of the 

 labelled sodium phosphate administered. Cohn and Greenberg^"^ found that, in 

 the course of 8 hours, only 60—70% of the labelled sodium phosphate administered 

 was absorbed. 



The above data inform us as to the lower limit of the rate of absorption of the 

 ■sodium phosphate administered, which can materially differ from the rate of 



(1) K. M.Henry and S. K. Kon, [Biochem. J. 33, 173 (1939)] emphasized recently 

 that a large part of the P present in the gut becomes fixed by intestinal bacteria 

 and is thus no longer available to the host. Bacterial bodies account for about 

 40% of the dry weight of rat faeces and P is a moie essential component of bacteria 

 than Ca. 



^2^ G. Hevesy and O. Bebbe, Kgl. Danske Vidensk. Selsk. Biol. Medd. (In print). 



^3^0. Artom, G. Sarzana and E. Segre, Arch. Int. Physiol. 47, 245 (1938). 



^*^ J. L. Dols and B. C. P. Jansen, Koninklijke Akad. van Wetenschappen 40, 

 i^o. 6, (1937). 



(5) W. E. Cohn and O. M. Greenberg, J. Biol. Chem. 123, 185 (1938). 



