GENERAL DISCUSSION 



BACQ : Ladies and gentlemen, in order to make our General Discussion 

 fruitful, and to guide it into the channel of the most pressing problems, 

 I wish to put before you a list of questions which follow logically from 

 all the material discussed at the symposium and around which, in my 

 opinion, it is advantageous to open the discussion. These questions are 

 as follows. 



I. Electron spin resonance spectra show that free radicals are 

 important in the primary mechanisms of radiation action. Using 

 this method one can obtain an experimental approximation to the 

 investigation of excited states. 



II. Mitosis is more radiosensitive than DNA synthesis. These two 

 processes do not have to be interconnected. Does anyone have any 

 ideas as to the mechanisms that regulate the rate of mitosis? 



III. Many primary lesions are reparable, even injuries to the nuclear 

 substance. Do these restorations occur as a result of natural meta- 

 bolic processes or by artificial action? 



IV. Chromosome breaks do not only occur as the result of direct 

 action, they must be regarded as secondary effects which are greatly 

 modified by the metabolic activity of the cell. 



V. There is not just one primary chemical injury caused by ionizing 

 radiation, but a whole series of changes which are most properly re- 

 garded as injuries to the structure (membranes, intracellular struc- 

 tures), which destroy the normal forms of contact inside the cell 

 between enzymes and substrates — the cellular auto-regulation of meta- 

 bolic processes. 



VI. Is the oxygen effect universal? It occurs in primary chemical 

 reactions. Part of the damage caused by ionizing radiation does not 

 depend upon oxygen. 



VII. The chemical protective substances have diverse action mecha- 

 nisms which can be simultaneous or synergistic. Each protective system 

 must be considered separately. One cannot draw simple conclusions. 



VIII. Some elementary physiological systems are radiosensitive, 

 some are very resistant. How can one explain this difference? 



If those present have no objection to the list I have proposed and also 

 no objections to allowing not only the members of the symposium, but 



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