728 ADVENTURES IN RADIOISOTOPE RESEARCH 



centage inhibition of the nucleic acid formation due to the action of 

 X-rays is, on the contrary, about the same in the liver of strongly growing 

 and adult rats and, furthermore, it is not greatly different from the 

 percentage inhibition observed in the case of the Jensen-sarcoma . 



Summary 



The metabolism of desoxyribonucleic acid has been determined in the organs 

 of 250 rats, aged between 3 days and 1 year, by using radioactivelly labelled 

 phosphorus as an indicator, and a study has been made of the effect of X-rays 

 on the rate of nucleic acid formation. 



Immediately after irradiation of adult rats with from 1500 to 3000 r, the for- 

 mation of new molecules of desoxyribonucleic acid in the liver, spleen and intesti- 

 nal mucosa is found to be reduced in the course of 2 hr to one-third to one-half, 

 i.e. to an extent similar to that found in the Jensen-sarcoma. The percentage of 

 newly formed desoxyribonucleic acid, in a period of 2 hr, in the hver and spleen 

 of 31/^ -day old rats is forty and ten times, respectively, the amount found in the 

 corresponding organs of adult animals. 



The percentage reduction in the formation of nucleic acid in the organs of 

 3 — 4 -day old rats due to the action of X-rays is not greatly different from that 

 observed in the organs of adult rats. 



