360 GENERAL DISCUSSION 



nature of the results of the action of physical agents — heat, oxygen, 

 nitric acid, water, etc. — on the ESR spectrum, on the one hand, and 

 the radiosensitivity of various objects on the other, led us to the 

 conclusion that the damaging action of oxygen is carried out only with 

 the participation of a certain amount of water. We have shown ex- 

 perimentally that water is necessary even for the realization of con- 

 cealed injuries, not connected with oxygen. 



Pepsin, irradiated in dry form, contahis concealed injuries which 

 appear when it is heated in aqueous solution. However, when incubated 

 in dry form, even at temperatures higher than 100°C it is impossible 

 to uncover concealed injuries that are known to exist. Thus water is, 

 in our opinion, a necessary participant for the realization of injuries 

 which are both dependent upon, and independent of, oxygen. 



In conclusion, I would Wke to point out that the existence of an oxy- 

 gen after-effect in solutions must compel us to approach with great 

 care the results of experiments carried out as it were anaerobically 

 but when the result of the irradiation is already verified in the presence 

 of oxygen. 



MARKOVICH : One further example to complete the list given by Gray. 

 Bacteriophage in cells up to the last moment of the latent period is 

 not sensitive to oxygen; bacteriophage outside the cell is also not 

 sensitive to oxygen. 



passynsky: In work carried out with Pavlovskaya we reached the con- 

 clusion that under the direct action of radiation, the oxygen effect is 

 governed by the transition of the irradiated oxygen into an excited 

 state O2* (with an energy of 5 to 6 eV) or in the state of the molecular 

 ion 02~, as a result of the absorption of an electron knocked out, for 

 example, from the protein. In both the states mentioned, the oxygen 

 can be an accepter of hydrogen (or of protons) and this affects the re- 

 distribution of hydrogen ions in the protein molecule. In the indirect 

 action of radiation (with a participation of molecules of the solvent) 

 the oxygen effect, at least in regard to the oxidation of the SH groups, 

 is quantitatively explained by the formation of HO2 radicals. It is 

 necessary, however, to take into account the reaction H02->H+-f02~, 

 which gives a second method for the formation of Oo" together with 

 the direct method 02 + e->02~. 



Thus, the influence of oxygen under various conditions of the action 

 of the radiation may have common mechanisms. The influence of the 

 oxygen following irradiation both upon the hydrogen bonds of proteins 

 and nucleic acids, and also on the formation of new products of radio- 



