216 A. V. LEBEDINSKY, V. M. MASTRYUKOVA AND A. D. STKZHIZHOVSKY 



of mitotic activity. However, observing respective data one may see 

 that there is no direct proportionality between the disturbance of DNA 

 synthesis and the radiation dose. 



20 



10 



5-3 



26-4 



(a) 



(b) 



Fig. 2.— -Tho number of dividing cells in E. coli cultures against the background of the 

 preliminary stimulation of nucleic acid synthesis and a certain inhibition of jirotein 

 synthesis (in percentage of un- irradiated control): 



(a) irradiation under normal growth conditions 



(b) irradiation against the background of a stimulated nucleic acid synthesis. 



This view may be supported by the experimental data of Libinson 

 and Konstantinova (1960). 



The authors worked with a truly non-exj^onential system and de- 

 termined the amount of nucleic acid in the liver and bone-marrow 

 (Schmidt and Thannhauser's method modified by Davidson) and the 

 rate of incorporation of ^'^P 4 hr after the introduction of 60 [iC of 

 Na2H32P04 solution per kg of animal. The average content of nucleic 

 acid in a single cell of the tissues was found by counting the number of 

 cellular nuclei per gramme of tissue. Possibly, the most valuable form 

 of exjDeriment is repeated irradiation with small doses. 



Libinson and Konstantinova found that exposure of animals at a 

 rate of 30 r per day led to some reduction (24 per cent of DNA-P per g 

 of liver tissue) in the early time intervals following the beginning of the 

 experiment (the total dose was 420 r). Then the content of DNA-P in- 

 creased and reached the initial values (the total dose was 2,490 r). 



The authors have also showed that the incorporation of ^sp into the 

 nucleic acids as determined by the state of the synthetic processes for 

 these substances in the liver shows an increase of specific activity of 

 2-2 for DNA, the total dose being 420 r (30 r for 14 days). After 900 r 

 the specific activity of the DNA was 26-4 per cent of the control. At 



