106 E. L. POWERS 



changes, and the general outUne of the survival curve depends on the ioniza- 

 tion density. I would like to show our preliminary data but they are as yet too 

 few. 



ALEXANDER: ^'\^ly do you think that ESR spectra are in some way related to 

 chemical transformations that cause damage? When ESR measurements are 

 taken, it is impossible to distinguish, whether the reactions in progress are 

 important to the cell or whether they are trivial biological processes. 



POWDERS : It is very difficult to distinguish which mechanisms are more important 

 and have crucial significance and which play a trivial role. I tried to present my 

 material here very cautiously. I said that the role of the free radicals may be 

 estimated from the biological effects. All the experiments listed above throw 

 some light on the biological effects also. ESR data are only used as supporting 

 evidence. 



ALEXANDER: It is with satisfaction that I hear that ESR methods could help in 

 the elucidation of biological problems. The data you have presented on the free 

 radicals are in favour of this method and justify the hopes it arouses. 



POWERS: My attitude towards EvSR methods is very reserved since here we enter 

 the sphere of physics. This method should be used very carefully and employed 

 as a control. I do not consider this method a universal one. 



