EXCRETION OF PHOSPHORUS 



543 



The average daily P excretion in the urine was found to be 950 mgni, the maxi- 

 mum of the specific activity of the urine P is reached after 5 hours (comp. Table 1 ). 

 The rapid decrease of the specific activity of the urine P, in the later stage of the 

 experiment, is due to the rapid decrease of the plasma P activity with time; the 

 labelled phosphate ions of the plasma being replaced by unlabolled ones ahea(i\' 

 present in the body, primarily in the skeleton and the muscles. The specific acti- 

 vity of urine P, which is derived from the plasma inorg. P, first increases with 

 time, due to the increased absorption of the labelled P administered into the 

 circulation. Besides, by interaction with ti.ssue phosphate, the plasma inorganic 

 phosphate also becomes "diluted" by unlabellcd P absorbed into the circ;ulation 

 from the food taken. The latter will therefore also influence the specific acti\it\' 

 of the urine P. 



In the experiment recorded in Table 2, the urine of a 22 years old male subject 

 was investigated. The subject took only a minimal amount of food and drink. 

 His daily urine excretion amounted to 610 cc, only containing 660 mgm P. 



Table 2 



In the course of the first day 6.8%, in the course of the second day 2.3% of 

 the labelled P was excreted through the kidneys. Higher figures were found in the 

 experiment on p. 542, 



In the experiment recorded in Table 3, we wanted to ascertain the amount 

 of labelled P excreted after a very short time. The male subject, 23 years old, 

 excreted daily 750 cc. urine containing 825 mgm P. 



