254 FACTORS INFLUENCING CELL RADIOSENSITIVITY 



irradiated with x-rays, glucose gives up some hydrogen which combines 

 with oxidative agents to form H2O2; so doing, it blocks these agents, 

 which are thus prevented from combining with other solutes. I take 

 this opportunity to approve Dale's statement regarding H2O2. I should 

 like, however, to point out that if the French school has attached great 

 importance to this substance (cf. 3) it is not always in order to endow 

 it with an active role in the production of the lesions. On the contrary, 

 we have emphasized (17) that H2O2 is, in many instances, a subsidiary 

 product whose presence attests that oxidizing agents have been diverted 

 from the lesion process. This is true to such an extent that in certain 

 cases increase in H2O2 means a decrease in the yield of the biological 

 reaction. 



The decrease in sensitivity of mice injected with a-tocopherol (10) 

 seems also to be connected with an oxidative process since this substance, 

 as well as glucose, is a strong inhibitor of peroxides. 



The protection afforded by oxygen acceptors is clearly displayed in 

 irradiation of aqueous solutions of strychnine (20). X-rays inactivate 

 this alkaloid by probable oxidation into genostrychnine with almost 

 complete loss of toxicity. Inactivation is not changed by the presence 

 of non-oxygen-accepting solutes such as NaCl, NaNOs, Fe2(S04)3, 

 SnCU, and saccharose. On the other hand, almost complete protection 

 is afforded by oxygen acceptors closely related to these solutes, that is, 

 NaN02, FeS04, SnCl2, and glucose. This experiment gives strong 

 support to the idea of participation of free oxygen in this inactivation 

 and of a very simple mechanism by which oxygen acceptors assure such 

 protection. 



PEROXIDASES AS FACTORS OF RESISTANCE AND RECOVERY 



Instead of decreasing sensitivity by diverting oxidating agents toward 

 acceptors, one can obtain the same result by destroying these agents. 

 For this purpose, peroxidases, and in particular catalase, come first in 

 mind. The preliminary results that I am about to describe reveal the 

 great complexity of the primary processes and especially their depend- 

 ence on cell metabolisms. Chemical destruction of the first irradiation 

 products implies either an immediate contact with the chemical, which 

 therefore must be present in the cell at the time of irradiation, or 

 sufficiently stable radioproducts. We do not yet know the magnitude 

 of the life span of oxidative free radicals, but experiments show that 

 catalase may remain active when added after periods of a minute or 

 even an hour. Accordingly it is possible to conceive of a general method 

 for decreasing certain radiation effects which would consist in treating 



