722 ADVENTURES IN RADIOISOTOPE RESEARCH 



An average sample of the tissue from the organ was used for isolating 

 the free P in the organ. In some instances the total P content of the 

 organs also was isolated. In these fractions also, one-fifth was used for 

 determining the radioactivity and one-fifth for colorimetric determination 

 of the P content. The radioactivity was measured by means of a Geiger — 

 Miiller counter. 



EXPERIMENTAL RESULTS 



The ratio of the ^^P content of 1 mgm of nucleic acid P at the end of 

 the experiment to the ^^p content present on the average in 1 mgm of 

 free P in the organ during the experiment was used as a measure of the 

 rate of formation of nucleic acid. The ^^P content of the free P in the organ 

 was determined at the end of the experiment. The values quoted in the 

 tables are, therefore, not an exact measure of the nucleic acid formation. 

 The rate of formation of nucleic acid in the organs of the rat w as determined 

 in collaboration with J. Ottesen^^\ taking into account the mean activity 

 of free P prevailing during the experiment. In the present study it was 

 desired to investigate the effect of X-rays on the rate of formation of 

 nucleic acid, and for this purpose it is sufficient to compare the activity 

 of the nucleic acid Pat the end of the experiment with the activity of the 

 free P in the organs at the same time. As we shall discuss later (p. 725), 

 the difference between the final and average activities of the free P in 

 the organs involved is not very considerable and in the case of the liver 

 is almost negligible. 



Table 1 exhibits the rate of formation of nucleic acid in the organs of the 

 unirradiated rat. Table 2 show the metabolism of nucleic acid determined 

 in the organs of the irradiated rat. 



We have not included any of the results obtained on 5-w^eek old rats 

 in Table 1 since no rats of this age have been irradiated; the figures in 

 Table 1 should be compared with those in Table 2, which contains data 

 on irradiated rats. 



The results which have been obtained with 5-week old rats are pre- 

 sented in Table la. 



Finally, a study was made of the rate of formation of nucleic acid 

 in the organs of adult rats which had been starved for 5 days. Table 

 lb shows that the rate of formation of nucleic acid was not much 

 affected by the fasting. 



It has already been demonstrated by one of us in collaboration with 

 J. OTTESEN^^Hhat the rate of formation of nucleic acid, in contrast to that 



1 G. Hevesy and J. Ottesen, Acta Physiol. Scani. 5, 237 (1943). 



