236 Barbara E. Holmes 



may be able to demonstrate a slight strain difference here. 

 At 1350 r there is very little effect on RNA or DNA synthesis 

 in either strain. 



It remains to be proved that the radioresistance still 

 persists in the Dittrich strain, and experiments are in progress 

 to test this point. At present, it seems that the effects on 

 DNA synthesis have very little to do with the radiosensitivity 

 of the tumours. These experiments are being repeated on 

 new strains sent from Germany. 



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Ord, M. G., and Stocken, L. A. (1956). Biochem. J., 63, 3. 



Pelc, S. R., and Howard, A. (1933). Acta radiol., Stockh., Suppl. 116. 



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DISCUSSION 



Roller: I cannot add anything more to Dr. Holmes' data except to 

 emphasize the fact that after irradiation there are chromosome breaks 

 in dividing cells of the regenerating liver. I may mention, however, the 

 very interesting fact that the number of mitoses which appear in re- 

 generating liver, treated with colchicine, is extremely high. We found 

 that 28-33 hours after hepatectomy, 85 per cent of the cells are under- 

 going mitosis. It seems that division must be extremely rapid and that 

 the duration of the mitosis is very short. 



