160 



ADVEXTURES IX RADIOISOTOPE RESEARCH 



ment. In comparing the rad. P content of different organs of the same 

 rat we are independent of the assumption that all the rad. P given 

 was actually eaten by the animal, though we are not, when we compare 

 the rad. P content of organs from different rats. The greater rad. P 

 content of the bones of the animals killed after the lapse of only a week 

 cannot, however, be clue chiefly to such a reason as this, because in that 

 case the rad. P content of the incisors would also be appreciably higher 

 in the case of rats killed after the lapse of one week. This is not the case, 

 as can be seen from the figures in Table 5. We must therefore conclude 

 that the rad. P taken up by the bones, and in exactly the same way 

 all the phosphorus taken up by the bones, has a certain chance of being 

 lost again. Indeed an uptake of phosphorus atoms by the bones of an 



Table G 



p. c. of rad. P 



taken, present 



ill 100 mprm 



of ashes 



weight of 



aslies of the 



organ in 



mgm 



p. c. of rad. P 



taken, present 



in the total 



ashes 



adult rat can only be explained by a corresponding process in the opposite 

 direction. Another example of the decrease in the active phosphorus 

 content of the bones with time is seen in Table 6. 



While the bones show a decrease in their rad. P content with time 

 and the molars no change to within the accuracy of experiments, the 

 incisors sliow a marked increase. The incisors of adult rats show a very 

 pronounced growth. The discussion of their behaviour is therefore better 

 postponed and will be dealt with in the next chapter, where experiments 

 on young rats are described. 



The results of an experiment carried out with two rats both killed 

 after 5 days time are seen in Table 7. 



1 The weight of the ashes of the liver was found to be very variable. 



