330 GENERAL DISCUSSION 



migrates to a "weak" position. This question has not yet been solved 

 in radiation chemistry, let alone radiobiology. The ESR method only 

 gives the properties of the unpaired electrons already formed. Both 

 may take place. One can, however, draw this conclusion from the 

 experiments, that for this migi'ation the conservation of the native 

 structure — of the regular network of hydrogen bonds — is necessary. 

 I think that the main possibilities for the ESR method in its applica- 

 tion to radiobiological, and to biological, problems in general lie in 

 the possibility of studying the weak, non-energy-controlling inter- 

 actions which I3lay such an impoi'tant part in biological processes. 



POWERS : It seems to me that it is absurd to suppose that ESR as an 

 analytical method can show us why irradiation produces injuries in 

 cells. But at the same time, one should not neglect that assistance 

 which the ESR method may provide in determining what these 

 injuries are. 



It is absolutely clear that a penetrating radiation produces in a cell 

 a whole series of effects. The ESR method, like spectroiDhotometry, is 

 not suitable for the study of all the physical and chemical changes in 

 cells. 



It is extremely important to apply all the physical methods which 

 are at our disposal. There may exist excited states of a radical and 

 other kinds of effects about which we still know nothing. 



It seems to me that in our work with the s23ores of bacteria we have 

 correctly applied the ESR method. And further, we have indeed 

 studied the correlation of the changes of the ESR spectrum with the 

 corresponding specific injuries due to irradiation. 



POLLARD : I will concern myself with two points. The first is the im- 

 portance of the ionization processes in comparison with excitation; 

 the second is some new data on the value of the S-S bonds in the irra- 

 diation of proteins. 



The work of Hutchinson with bovine serum albumin has shown that 

 no inactivation is observed below 1 1 eV, although this energy is much 

 higher than is necessary for excitation. 



Subsequently, the work of Setlow on u.v. irradiation in a vacuum 

 showed that the quantum yield does not increase and does not approach 

 unity provided that short waves of approximately 1,300 A are not used. 

 This radiation can ionize. Thus ionization is 100 times more effective 

 than excitation. 



In regard to the second point : the enzyme, ribonuclease, in the native 

 state is not digested by trypsin. If it is subjected to irradiation, then 



