General Discussion 307 



Popjak: May I contribute to that? I think the real significance of 

 those experiments might be that the phenomenon was observed 

 during irradiation, and Hug has observed the luminescence while the 

 bacteria were irradiated. Immediately on starting irradiation the 

 luminescence decreased, when he stopped irradiation it returned, and 

 so on, although I think that with higher doses the luminescence did 

 not quite return to the original starting value. The importance of 

 this is that it is well worth thinking of experimentation in which we 

 try to look at enzyme reactions while irradiation is going on. 



Laser: I have mentioned before that the enzyme notatin is inacti- 

 vated by X-rays more strongly if irradiation takes place in the 

 presence than in the absence of its specific substrate (glucose). I 

 should add that I conclude that the enzyme is most sensitive to 

 X-ray damage at the stage of a semiquinone. 



Dale: Which would fit in with what I mentioned. 



Latarjet: Dr. Dale, may I ask you if your chain reaction of thiourea 

 takes place in the absence of oxygen? 



Dale: On the contrary, it takes place in the presence of pure 

 oxygen. If you decrease the oxygen tension the dose-rate depend- 

 ence is not abolished, but the absolute effects are getting smaller and 

 smaller. In the absence of oxygen there is hardly any effect. 



Mitchell: One point which we have not discussed at all at this 

 meeting, and which I think might be of interest, is the relative 

 biological efficiency of different radiations for metabolic effects, 

 particularly the comparison of effects of radiation with low and high 

 specific ionization, in biosynthesis of nucleic acids. There are the 

 experiments of K. G. Scott (1946, Radiology, 46, 173) and the more 

 recent experiments of A. Howard and S. R. Pelc (1953, Heredity^ 

 Suppl. to Vol. 6, p. 261). I wonder if people consider that further 

 information might be obtained from a special study in this direction. 



Howard: To follow up that suggestion with regard to effects of 

 different types of radiation on DNA synthesis in tissues would be 

 extremely useful. We have very little information on this point, and 

 it would give us one obvious means of sorting out the mitotic delay 

 and cell death on the one hand, and the effect on DNA synthesis on 



the other hand. 



Haddow: When Banting discovered insulin, or most probably 

 rediscovered it, about 1922, he was expected by the public to make a 

 great series of further discoveries along the same lines, including a 

 cure for cancer, the study of which he took up shortly thereafter. I 

 remember Sir Henry Dale telling a story of how, round about 1923, 

 he was phoned up in great excitement by a Press reporter to know 

 was it true that Banting had discovered a cure for metabolism. We 

 may not have discovered the cure for metabolism, but we may be on 



