RADIATION DAMAGE TO CHROMOSOMES 207 



ALEXANDER: Have you data inclioatiufi that post-exposuiH- tiHvxtment. dccroasing 

 incidence of the mutations, facihtates simultaneously the repair of the damage 

 leading to the cell death? Ts there a similarity between the process of mutation 

 repair and that of repair of otlier cell damage? 



HOLLAENDER : I bcHeve tliat there is a difference. However, at present I cannot 

 answer this question because I do not have the necessary experimental data. It 

 is possible that in order to solve it, it would be necessary to work out a special 

 method. 



I believe that mutations differ from the processes of the general cell damage and 

 I think that the processes of the initial damage in these phenomena are different. 



bacq: Did the oxygen effect occur when Aspergillus terreus spores were pro- 

 tected? For me it is important to know, whether this compound protects against 

 oxygen or not. 



HOLLAENDER : We have not yet studied it. 



BACQ: Do not you think that it is an interesting field for investigation? 

 HOLLAENDER: Every investigation consists of many stages. I think it would be 

 intei'esting to study this question. It would not be very difficult to solve it. 

 i^EBEDiNSKY: Would you not agree to apply the term "extracellular factors" to 

 those compounds which affect the occurrence of back -mutations? And, if so, 

 have you not tried to classify these extracellular factors? 



HOLLAENDER: In our work all our attention was focused on the exi3eriments 

 which permit quantitative estimation. We are sure that the mutation process 

 is affected also by extracellular factors. To study this problem it is possible to 

 irradiate only cytoplasm but for this much greater doses should be applied. At 

 present no precise method of studying these changes is available. We transferred 

 nuclei into the irradiated cytoplasm, but have not as yet obtained clear-cut 

 results. I would prefer not to speak about it now. I am sure that methods of 

 studying the cytoplasm could be devised, which would help to study qualitative 

 changes. ^ , 



HOLMES: I would like to point out that in sperm owing to metabolic processes 

 there is enough energy. I believe that you probably mean some special metabolic 

 processes when you say that the processes of mvitation repair in sperm are im- 

 possible becavise the metabolism is lacking. 



HOLLAENDER: I shoulcl in this connection point out that metabolism in the sperm 

 differs from that in spermatogonia. Maybe metabolism which occurs in sperm, 

 caimot stop the processes occurring after the irradiation. However, I am not con- 

 vinced that it is so. There may be alternative approaches which would make 

 it possible to interpret these facts otherwise. 



gray: I would like to make one remark with regard to the different effects ob- 

 tained when sperm or spermatogonia were exposed. In particular, when a lack of 

 repair in sperm is stated, is it not due to such changes, produced by irradiation 

 of sperm and ovum, which are irreversible? But it is not of course a mutation. 

 You have said that this is the first work on mutation repair — of course it should 

 be continued. 



I would like also to say several words about Dr. Alexander's remark. Maybe it is 

 worthwhile to remind ourselves that it is necessary to distinguish between the 

 effects on the incidence of mitosis and on the duration of the separate phases. I 



