172 M. ERRERA 



ERRERA : On the picture given here results of the experiments using whole cells 

 were presented. After that isolated nuclei were used. 



KUZIN : If I understood you correctly, in the experiments with isolated nuclei 

 you found apjaroximately 30 per cent inhibition : further increase in the irradiation 

 dose produced no increase in the effect studied. At the same time using whole 

 cells and tissues one may obtain considerably more inhibition. Do you not think 

 that the difference is accounted for by the role jolayed by the cytoplasmic 

 elements? 



ERRERA: I am not sure whether we realize what is occurring in the nucleus. But 

 it is a fact that, for protein synthesis, inhibition in intact cells occiu-s in 90 min. 

 The purpose of this stv;dy was to determine the most sensitive process. 



MOUTON : May it be that the changes you have observed are caused by the changes 

 in the pH of the medium brought about by irradiation? 



ERRERA: I do not think so, since strongly buffered solutions were used throughout 

 the experiments. 



MOUTON : It seems possible that there may be a connection between the radiation- 

 induced breakdown and acid autolysis. 



HOLLAENDER: You sjioke about inhibition of the synthesis of the nucleic acids 

 and proteins. How is this related to mitosis? 



ERRERA: Under normal conditions the mitotic index amounts to 5 to 7. It seems 

 to me that the nuclei we studied should be considered as being in a resting phase, 

 not in mitosis. 



TOBIAS: You said that RNA synthesis is inhibited by 30 per cent. How is this to 

 be understood? Does it mean that 30 per cent of the nuclei are not taking part in 

 the synthesis, or that synthesis in all the nuclei is inhibited by 30 per cent? 



ERRERA: Autoradiography has shown that all the nuclei have been affected 

 equally. 



