266 CORNELIUS A. TOBIAS, TOR BRUSTAD AND THOMAS MANNEY 



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DISCUSSION 



ALEXANDER: Why does the ploidy affect radiosensitivity differently for yeasts 

 than for j^lants? 



TOBIAS : With the ploidy increases the effect of the recessive lethals goes down, 

 whereas that of the dominant ones increases. The outcome is determined by the 

 interaction of these two processes. There is another yeast line, where the ploidy 

 effect is different. 



pollard: It is very imj)ortant to consider the effect of S -irradiation by heavy 

 ions, using Bohr's formula, as it was used by Lee and others. This was done for 

 /3-galactosidase by Hutchinson and Dolphin. They have shown that only one 

 inactivation value may be used to explain the results obtained while using 

 S-rays as well as irradiation by very heavy ions. The work with trypsin recently 

 carried out in Yale, could also be intei-jDreted from this standjooint. 



As for the oxygen effect, since the ciuantity of S-rays varies in inverse ratio to 

 the square of the energy S-ray intensity will be higher for lower energy radi- 

 ations, showing very small oxygen effect. So according to these two considerations, 

 the results of these exj^eriments do not rec|uire in themselves assumptions about 

 any additional effects. For other exiDerimental data this may be the case, but to 

 account for the results presented here there was no need for such effects. 



TOBIAS: I agree with Dr. Pollard. Of course, S-rays should be studied carefully. 

 I may only repeat the thesis, that we cannot explain all the effects observed by 

 this phenomenon alone. 



marcovich: It is very interesting that when heavy particles were vised, a pro- 

 tective effect was found and oxygen did not exert any influence. 



Did you study the influence of glycerol on other organisms beside yeast? 



TOBIAS : We have not used glycerol for other organisms. We are continuing this 

 work; it has proven to be very com23lex. 



MOUTON: I would like to a.sk about the effect of pH. 



