320 V. N. TARUSOV 



yield. The diflferences in radiosensitivity by irradiation in oxygen are 

 greatest in agar cultures (in the atmosphei^e) where the LD50 is of the 

 order of 100 to 160,000 r for the diploid and 4,000 r for the haploid. 



For irradiation in water suspensions in oxygen it is 40,000 r for the 

 diploid LD50. and 4.000 r for the haploid. It shows that, in suspensions 

 of diploid cells, an indirect effect, through the products of water radio- 

 lysis, prevails, on which an increase in oxygen pressure has no effect. 



In irradiation of agar cultures a part is played by the reactions in- 

 directly induced in the organic phases of the cells. In haploid cells the 

 physico-chemical conditions are such that reactions in organic phases 

 are easily induced by direct irradiation and the increase of water in the 

 external medium cannot increase the lethal effect. This reflected in the 

 lethality curves at lower oxygen pressure in water suspensions. From 

 that point of view one should analyse the primary reactions in multi- 

 cellular organisms. As has been pointed out the lethality curves in con- 

 nection with oxygen pressure have a marked threshold character in 

 mammals, insects, etc. (Fig. 1). 



This makes it possible to conclude that primary, oxidizing radio- 

 chemical reactions arise and develop in the main in the organic phases 

 of the cells and this fact apparently determines high radiosensitivity. 



The considerations given above are confirmed by data, constantly 

 published, which establish the appearance of active lipoperoxides in 

 irradiated organisms (Morgan and Philpott, 1954). 



It has been demonstrated that the formation of these ])eroxides can 

 be discovered during irradiation and that it is hindered by protective 

 substances. 



We have studied kinetic regularities in the formation of lipoperoxides 

 in the liver of rats after various doses of irradiation. Malts (1960) has 

 shown that during irradiation tliree chain reactions in the lipids of the 

 liver with different kinetic parameters take place. The changes in the 

 amount of peroxides correspond to the kinetic accumulation of inter- 

 mediate ]iroducts of chain reactions, i. e. the amount of peroxide is de- 

 termined by the rate of the reaction at the given moment (Fig. 6). 



There are grounds for the assumption that these reactions in bio- 

 lipids are connected with the destruction of anti- oxidants always 

 present there. We have established that, after irradiation, there is a 

 gradual decrease of anti-peroxidants in the lipids of the liver of rats and 

 mice (Zhuravlev, 1960 ; Malts, 1960) parallel to the reaction of radiation 

 oxidation. 



As we know, oxidizing reactions are considerably slower in the 

 I)resence of anti-oxidants. though not completely stopped. A ninnber 

 of investigations have shown that a slight decrease of the anti-oxidant 



