ACCELERATED HEAVY IONS ON ENZYMES AND YEASTS 207 



TOBIAS : Tills is also a very dinicult (lucstion. since water itself changes the process. 



ARDASHNiKov : Have I undeistood you correctly that the addition oi" the pro- 

 tective agent in some cases brings about an increase of the sensitive volume? 

 If this is so, then how shoukl it be understood, since addition of the protective 

 agent should increase the lethal dose, while increase of the dose must always 

 jDroduce a decrease of the sensitive volume, whatever be the modification of the 

 basic formula for the calculation of the sensitive volume. 



TOBIAS: In Fig. 1, I showed only the cross-section; the effective dose was not 

 given. When the cross-section increases, it means that the same effect may be 

 produced by a smaller dose. 



GRAY: I congratulate Dr. Tobias on his excellent work on the effects of highly 

 ionizing heavy particles. 



I wovild like to make a remark connecting with Dr. Marcovich's statement. 

 Observations made by Dr. Dewey on bacteria Serratia marcesceus, to which I 

 have already referred in this symposium, are in good agreement with Dr. Tobias' 

 data with regard to the glycerol effect on damage caused by particles with low 

 linear energy transfer. We observed a strong protective effect by glycerol (about 

 two-fold) even if the bacteria were under strictly anaerobic conditions during 

 iiTadiation. Since, however, aerobic cells are protected by glycerol to about the 

 same degree when equilibrated either in 100 per cent oxygen or in 1 per cent 

 oxygen, we think that the mechanism of protection is not connected with com- 

 petition between glycerol and oxygen for the radicals. 



