EFFECT OF X-RAYS ON NUCLEIC ACID I.V THE RAT 



727 



Table 3. — Comparison of the Activity of 1 mgm of 

 Nucleic Acid P in Unirradiated Rats, Expressed 



AS A PERCENTAGE OF THE ACTIVITY OF 1 mgm OF FREE 



Phosphorus in the Organ or Plasma, with the Cor- 

 responding Vali'e in Irradiated Rats 



Organ 



Ratio: unirradiated — irradiated 



Compared witti 



free P in the 



organ 



Compared witli 



free P in the 



plasma 



Liver 



Spleen 



Intestinal mucosa 



2.3 



2.5 

 2.3 



Formation of Nucleic Acid in the Liver of 3V2 — 4V2-day old Unirra- 

 diated and Irradiated Rats 



We have extended our investigations to the determination of the 

 nucleic acid formation rate in the liver and spleen of strongly growing 

 3 — 4 day old rats. 



Twenty-seven rats aged S^v, days were each injected with 0.05 cm-^ 

 of a solution containing ^^p (activity 2 //c). i\fter 2 hr the rats were 

 killed and the nucleic acid P was isolated, as also the free P, from the 

 liver and spleen. The formation of nucleic acid, determined by means 

 of the activities of these fractions, can be seen in Table 4. 



Table 4. — Formation of Nucleic Acid in the Organs of Twenty-seven Si/o- 



day Old Rats in a Period of 2 hr 



In order to determine the effect of X-rays on the formation of 

 nucleic acid in the liver of strongly growing rats, we irradiated seven 

 3— 4-day old rats with 2000 r immediately before injecting with radio- 

 active phosphate. The rate of formation of nucleic acid during a 

 period of 2 hr was found to be 0.81 per cent and therefore less than half 

 the value (1.96) determined in the unirradiated animals. 



This magnitude of nucleic acid formation in the liver of unirradiated 

 or irradiated strongly growing (4-day old) rats is an order of magnitude 

 greater than the formation found in the liver of adult rats. The per- 



