KXCHANCK OK VHOSIMIOI? IS IN rKKIH 



IHl 



Tablk 13. 



The fresh tissue of the incisors contains more labelled I^ than equal 

 weights of either the molars or the tibia, but comparing the ashes the 

 tibia has a larger labelled P content than both the incisors and the 

 molars. A comparison of the labelled P content of the 

 ash is in general preferable to that of the fresh tissue, 

 the former comparison giving information about the 

 percentage of phosphorus atoms replaced by labelled 

 ones. The total P content of the ash of the incisors 

 varies between 19.6 and 20.0%, and that of the molars 

 and the tibia is only slightly smaller, about 18%. A 

 closer analysis of the tibia revealed the parallelism 

 already mentioned between the content of organic 

 tissue and labelled phosphorus; that is shown in Table 

 14. The rat was killed 3 days after the administration 

 of the labelled P. 



As seen from the figures of Tables 13 and 14 the 

 head of the tibia has exchanged a part of its phos- 

 phorus content eight times as large as that exchanged by the 

 molars. 



Furthermore we compared the labelled P content of the incisors, 

 the molars, and the tibia in the case of a rat weighing 220 gm killed 

 1 hour after the labelled phosphorus had been administered by sub- 

 cutaneous injection. The results are seen in Table 15. The incisor was 



02 



02 



Fig. 4. 



Table 14. 



