CELL DAMAGE IN THE MAMMALIAN RADIATION SYNDROME 



247 



experiments on mouse cornea. Thus the number of cells having no 

 bridges and fragments in the cornea of mice irradiated in an atmosphere 

 of carbon monoxide was two times and the mitotic index 1 -5 times that 

 of the unprotected control (Shapiro and Konstantinova, 1959). 



(2) The action of most protective agents is due to hypoxia of the 

 tissues. Some S-containing substances (monothiols and thiourea deri- 

 vatives) exert their action without causing hypoxia. 



A decrease of 02-tension during irradiation is known to weaken the 

 radiation effect. The universality of this phenomenon led to the idea 

 that the protective action of various agents could be explained by the 

 hypoxia induced by them. However, until lately there were no direct 

 experiments showing that protective substances change O^-tension in 

 tissues. That is why in 1957 we began experiments in which the influ- 

 ence of protective substances on the survival of y-irradiated mice at 

 different time intervals after drug-treatment was compared with the 

 action of these agents on 02-tension measured by a polarographic 



o^ 20 



10 20 30 40 50 60 70 80 90 100 

 Decrease of Oj-tension and survival (per cent) 



Fig. 7. — 1, survival of mice exposed to 900 r of y-rays of ^oCo at different rectal tem- 

 peratures, la, as 1 but taking into account the mice that died after cooling. 2, 02-tension 

 (percentage of the initial level) in the spleen (J^, A, after cooling and rewarming, resp.). 

 3, the same in the liver (9, o, after cooling and rewarming, resp.) 



