CHEMICAL SPECIES INDUCED BY X-RAYS IN CELLS 105 



BACQ : At what time after the exposure to radiation were the spores treated with 

 nitric oxide or hydrogen sulphide? 



ro\\EKS : A\'e found tliat for 1 -5 to 3 In- at room temperature the relative concen- 

 tration of the radicals we dealt with did not change considerably. This j^oint was 

 carefully studied and in our last paper the kinetics of these phenomena at different 

 temperatures are given. 



BACQ : It is a great pity that mammals are not bacteria and could not be fitted 

 into yoxir data. 



HOLLAENDER: Did you study any physiological or genetic phenomena? 



POWERS : We were interested in morj^hological characteristics of the colonies and 

 tried to get a deeper insight into the j^hysical i^arameters which are of importance 

 here. Very little attention has been given to other biological processes outside 

 the scope of our investigation. 



TARUSSOv : Can nitric oxide be regarded as an inert substance with regard to the 

 objects you studied? 



POWERS: \^Tien oxygen is excluded the nitric oxide by itself is not toxic for 

 bacteria. In other words the presence of nitric oxide i^roduces no harmful effect 

 on the sjDores ; it does not affect them in any way. The same may be said for hydro- 

 gen suljihide. 



I should like also to answer Dr. Gray's question. When we use nitric oxide, 

 it niust be carefully removed afterwards from the system. Otherwise some toxic 

 phenomena may occui'. 



TOBIAS: From the sm'vival curve it may be seen that a lethal effect is present. 

 Can you determine the quantity of the radicals in one spore, in ten thousand or in 

 other great quantity of spores? "WTiat is the precision of the experimental tech- 

 nicjue you have used? 



POWERS : We are very hajopy that we can seek the advice of the jDhysicists who 

 use ESR methods. 



passynsky: Is it jDossible to determine the radicals' concentration using more 

 simple substances or some fractions of the spores studied? Or do they appear 

 only when all the complexity of the .spores' composition is retained? 



POWERS : Of course, there is the possibility of carrying out these measurements 

 on cellular fractions, but we have not done it. I may call your attention to the fact 

 that quite recently in Dr. Gordy's laboratory there was observed, while studying 

 caesin, an increase in the size of the doublet signals. It is almost identical to 

 what I have shown today for spores. 



PASSYNSKY : Was the quantity of the radicals determined directly vuider the beam? 



POWERS: No. All the measurements were performed after the exposure and, by 

 the way, in c^uite another building. Experimental material was transferred to 

 other conditions. 



BARENDSEN: What could you tell about the cross-section and the effects of the 

 linear energy transfer? 



POWERS : Our experiments with irradiations of different ionization density were 

 carried out together with Dr. Tobias' gi-oup in California using the HILAC. 

 At present I can tell you that as linear energy ti'ansfer increases, radiosensitivity 



