668 



ADVEXTURES IN EADIOISOTOPE RESEARCH 



acid P the specific activity of the cellular free P. The figures for the size of 

 the extracellular space of the organs were taken from a paper by Manery 

 and Hastings (1939) and it was assumed that the labelled phosphate 

 concentration of the extracellular fluid is identical with the labelled 



'6 -1 



8- 



■ Doily percentage renewal of 

 desoxyribose nucleic acid 



0> 



a 

 S 





•o 



c 

 o 



Fig. 1. 



phosphate concentration of the plasma water. The correction for the 

 presence of labelled phosphate in the extracellular space was largest 

 for the testes, but even in this case only 12 per cent of the value stated 

 in Table 1. We did not correct the specific activity found for the free P 

 of the brain in view of the uncertainty prevailing as to size and compo- 

 sition of the extracellular fluid of the brain. Therefore, it is possible 

 that the rate of renewal of the brain nucleic acid is not slightly larger, 

 but smaller than the corresponding value found for the kidneys (cf. 

 Table 2). 



The percentage ratio of the specific activity of nucleic acid P and 

 free P (the percentage renewal of the nucleic acid) in different organs 

 is seen in Table 2 and Fig. 1. The highest percentage of new nucleic 

 acid is found in the small intestine, while the lowest figure is shown 

 by the brain. Remarkably low figures are found for the liver. In the 



