364 GENERAL DISCUSSION 



DUBININ: The study of the chemical i^rotective agents can be con- 

 sidered in the analysis of the nature of the primary effects of radiation 

 upon genetic material. In the work of Dubinin, Sidorov and Sokolov, 

 this method was applied to living cells. By utilizing the phenol- 

 ascorbic acid reaction with hydrogen peroxide, we have obtained 

 free OH radicals chemically within the nucleus of the living cell. 

 These radicals have given rise to a sul)stantial genetic effect. In the 

 nuclei of the cells of onion rootlets about 20 per cent of chromosome 

 arrangements were found. In earlier work on the production of chro- 

 mosome arrangements by visible light Dubinin, Sidorov and Sokolov 

 showed that the iodide ion and certain other substances protect the 

 nucleus from damage by the photodynamic process. We have used this 

 protection to study its influence on the genetic effect from chemically 

 derived radicals. By introducing into the cell ions of iodide, bromide 

 and hydroquinone, quinone, hyposulphite, and thiourea, we have dis- 

 covered that all these protect the chromosomes from chemically 

 derived radicals. 



However, it was discovered from experiments with X-irradiation 

 that iodide and bromide ions have no defensive effect. Dury and Kalam 

 in their pajjer proved that iodide ions penetrate the nucleus. Thus, the 

 interception by iodide and bromide ions of the free radicals which 

 arise in the radiolysis of water does not protect the chromosome from 

 the effect of radiation. This points to the predominance of the direct 

 action of the radiation on the chi^omosomes. Mekshenkov in our labora- 

 tories, while studying the effect of radiation on DNA solutions of various 

 concentrations, showed that for low^ concentrations, when the indirect 

 effect of the radiation prevails, the iodide and bromide ions provide a 

 protection close to 100 per cent and in solutions of high DNA con- 

 centration, these ions do not protect the number of DNA molecules 

 being measured. 



This experimental analysis confirms the coiTectness of the forecasts 

 made by many authors concerning the enormous significance of the 

 direct action of the radiation on chromosomes. The experiments of 

 Alexander carried out Mith dry polymers have great value. It follows 

 from his data that for DNA molecules in chromosomes, one must 

 expect the predominance of the direct radiation effect. 



All this shows that wdien working out the problem of the chemical 

 protection of genetic material, one must take into account, as a main 

 factor, the direct effect of the radiation and not the reactions for 

 competition for the free radicals. 



TARUSOv: In the survey article by Rachinsky and Mozzhukhin in 



