EXCRETIOX OF PHOSPHORUS 549 



of these experiments did not suffice to carry out such a calculation. To enable 

 us to determine with sufficient accuracj' the ratio of the specific; activity of the 

 urine P and the faeces P, we administered labelled sodium phosphate having an 

 activity of about Viooo milliCurie to a female subject and investigated the urine 

 and faeces collected after the lapse of 7 and 8 days resp. As the faeces, collected 

 after the lapse of 8 days, actually accumulated in the bowels at a somewhat earlier 

 date, it is advisable not to compare urine and faeces collected the same day, but 

 to compare the faeces with the urine collected one day previously. The result 

 of this experiment is seen in Table 8. The specific activity of the total faeces P 

 is only 24% of that of the urine P, the faeces P must therefore to a large extent 

 originate from non-absorbed food, which is the only source of non-active P. It 

 follows from the above figure that 76% of the P present in the faeces of the human 

 subject in question is non-absorbed P, the rest originating from the body proper. 

 This is, however, not to be interpreted as indicating a phosphorus absorption 

 of the food taken amounting to only 24°o- When interpreting the above figure, we 

 must take into account that the P excreted through tht kidneys amounts to about 

 twice of that lost through the bowels, and the sum of both values represents the 

 total P present in the food, if we assume that the subject in question is in P balance. 

 We then find that only 25% of the total P present in the food was not absorbed 

 into the circulation. 



Table 9. — Specific Activity of Urine P and 



Faeces P of a Female Subject 28 Days after 



Administration of Labelled Sodium Phosphate 



BY Subcutaneous Injection 



'■' 18»/„ of the total P found in the faeces was residual P obtained after tlie removal of the acid- 

 soluble P (mostly calcium piiospliate) and tlie traces of phosphatide P present. Tlie specific activites of 

 the different P fractions differed only to a minor extent. 



Through the courtesy of Dr. Kjerulf-Jensen, who is investigating the P 

 metabolism of a human subject by making use of radioactive P, we could investi- 

 gate the faeces P and the urine P, collected 28 days after administration of labelled 

 P. The results are seen in Table 9. From the ratio of the specific activities it follows 

 that 20% of the P percent in the faeces was of endogenous origin and that of the 

 total P present in the food 27% was not absorbed into the circulation. 



Excretion by rats 



We determined also the ratio of the specific activities of the uiine P and faeces 

 P excreted by a rat to which labelled sodium phosphate was administered, by 

 subcutaneous, injection, 98 days previously. The results are recorded in Table 

 10. The rate of the specific activities is 2.4, thus 59% of the P found in the faeces 

 originates <rom non-absorbed food P. The faeces P making 57% of the total 



