EFFECT OF X-RAYS ON NUCLEIC ACID IN THE RAT 



725 



trate rapidly into the cells and then gradually leave again. The rate of 

 penetration of the labelled phosphate into the spleen cells is slower 

 and should not differ very considerably from the rate of penetration 

 into the cells of the Jensen-sarcoma, where the final value of the specific 

 activity of the free P was found to be about 25 per cent greater than 



Time after injection 

 of "n^ (ill-) 



Percentage of the injected 



^^P present in 1 nigm of 



free liver P 



¥2 

 1 



2 



2.3 



2.8 

 2.1 



the mean value. If the final value 2.5, in the last horizontal row of 

 Table 1, is multiplied by about 1.25 we approach the percentage renewal 

 of nucleic acid in the spleen taking place in a period of 2 hr. 



We also determined the variation in the specific activity of the free 

 phosphorus in the liver and spleen of 31/2 day rats with time. The follow- 

 ing percentages of the ^^p injected into each rat (0.05 cm^ of radio- 

 actively labelled physiological sodium phosphate solution), were found 

 in 1 mgm of free P as shown : 



In these experiments also, the final value of the specific activity of 

 1 mgm of free liver P differs only a little from the mean value of the 

 activity during the experiment. A comparison of the values obtained 

 for the spleens of 3I/2 day rats with those for adult rats (cf. Table 3) 

 yields the result that the phosphate ions penetrate into the spleen cells 

 of 3I/0 day old rats at about the same rate as into the liver cells, whereas 

 the liver cell walls of the adult animals are appreciably more permeable 

 to phosphate than are the spleen cell walls. 



Effect of Irradiation on the Rate of Formation of Nucleic Acid 



Table 2 contains data for the rate of formation of nucleic acid in the or- 

 gans of irradiated rats. The animals were exposed to total body irradiation, 

 except that the head was covered with 5 mm thick lead sheet. The time 

 of irradiation amounted to 20 — 40 min. Irradiation was performed with 



