150 



ADVENTURES IN RADIOISOTOPE RESEARCH 



Rats were fed with a few milligrams of sodium phosphate containing 

 J5P as indicator. The radioactive phosphorus present in the urine and 

 faeces was then investigated for a period of a month. The result is shown 

 in Fig. 1, which shows the percentage of the 2 mgm of phosphorus 

 taken, found daily in the excrements. The rat was killed, and, after 

 ignition, the phosphorus content of the different organs was investiga- 

 ted. The result of an experiment in which the rat was killed 22 days 

 after being fed on active phosphorus is seen in the first column in Table 1 . 

 The largest part of the phosphorus taken is present in the bones, and 

 the smallest in the kidneys. When, however, we take into account the 

 very different weights of the different organs and calculate the phos- 

 phorus content of the latter per gram after drying, we obtain a very 

 different picture, as seen from the second column in Table 1. The spleen, 

 kidneys, and the brain are found to contain per gram most of the active 

 phosphorus. During one of the experiments, the rat produced six off- 

 spring on the seventh day, of which five were eaten by the mother ; 

 this caused a large increase in the active phosphorus content of the 

 excreta in the following three days. The presence of 2 per cent of the 

 2 mgm active phosphorus taken by the mother was revealed by the 

 analysis of the remaining offspring. 



Table 1. 



Distribution of the active phospho- 

 rus IN the rat 



The active phosphorus content of the urine and faeces shows great 

 fluctuations during the first few days after the intake of the preparation. 

 Later, it becomes fairly constant; and we have obviously to deal with 

 the excretion of phosphorus which has already been deposited for a 

 while in the skeleton, the muscles, or other organs, and wdiich has been 

 displaced again. From our experiments, it follows that the average 

 t ime which a phosphorus atom thus spends in the organism of a nor- 

 mally fed rat is about two months. This is also supported by the fact 

 that rats killed about a month after the intake of phosphorus contain 

 only about half the active phosphorus found in those killed after a weeks 

 time. This result strongly supports the view that the formation of tiic 



