IMMEDIATE EFFECTS OF X-RAYS ON LIVING CELLS 



13( 



labelled and are indicated here by black dots. The figure shows that 

 the normal cells had all attained the full 8/i amount of DNA G hr after 

 labelling whereas the irradiated cells had only completed about half 

 their synthesis. 



• Labelled nuclei 

 n Unlabelled nuclei 



c 

 =] 

 O 

 u 



O 



60 

 50 

 40 

 30 



20 



10 





J 4) 



2N 



4N 



PBN^ 



o 2 



200 600 1,000 1,400 1,800 

 DNA (abltrary units) 



3 

 _V 



u 



13 

 C 



V 



a. 



(/> 



60 

 50 

 40 



30 

 § 20 



2 10 

 o 



2N 



(Radiation dose 3,000r) 



• Labelled nuclei 



A Labelled divided nuclei 



n Unlabelled nuclei 



200 600 1,000 1,400 1.800 

 DNA (arbitrary units) 



Fig. 2. Plot of grain counts against DNA content of the same hepatic nuclei of a rat 



given tritiated thymidine at 1 7 hr after hepatectoniy and sacrificed (5 hr later. 



In absolutely similar material we have now made a simultaneous 

 study of the synthesis of nucleic acid and of the residual protein to 

 which the nucleic acid is found to be attached after removal of the 

 histones. The synthesis both of this protein and the histones normally 

 seems to take place at much the same time as the synthesis of the DNA 

 in regenerating liver, since the uptake of lysine and of arginine into the 

 proteins is then three or four times higher than that in resting liver 

 tissue. 



