L. H. GRAY 



the formation of peroxides which decompose thermally. Thus, when a 1 per 

 cent solution of polystyrene in chloroform is irradiated, the presence of 

 oxygen enormously enhances the number of breaks which are induced in the 

 polymer chain compared with an anaerobic irradiation, but nitric oxide has 

 no such effect (A. Chapiro — personal communication). Irradiated Perspex is 

 not bleached by nitric oxide as it is by oxygen (Boag and Gray — unpublished). 



Professor Porter has drawn my attention to the fact that the two gases, 

 oxygen and nitric oxide, are equally efficient in producing spin forbidden 

 transitions, such as between singlet and triplet states, as well as in transfer 

 to and from metastable states. This possible role of oxygen and nitric oxide 

 in radiobiology would appear to deserve very serious study. 



Finally, reference should be made to the theoretical studies of Platzman 

 and Franck"^, who adduce cogent reasons for believing that the electric 

 fields which arise through the separation of positive and negative charges 

 at the instant of ionization may lead to an important measure of secondary 

 hydrogen bond breakage in proteins and other polar macromolecules. It is 

 conceivable that the readiness with which electrons become attached to 

 oxygen and nitric oxide may influence the magnitude and duration of such 

 electric fields. 



It may well be that when the story of oxygen controlled radio-sensitivity 

 is fully unfolded, each attribute of this remarkable molecule — physical, 

 chemical and biochemical — will be seen to be critical to some aspect of the 

 phenomenon which we have had under review. 



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