CELL DAMAGE IN THE MAMMALIAN RADIATION SYNDROME 253 



strongly than the transi^ort of oxygen to tissues. It may be suggested 

 that this event does not take place in heterothermous animals irradiated 

 under lowered body-temperature during hibernation; no hypoxia of 

 tissues is brought about under these conditions and noj^rotection occurs. 



A number of jDrotective agents (monothiols and thiourea derivatives) 

 possess a strong protective action but do not cause hypoxia. This fact 

 does not exclude the possibiHty that the mechanism of action of these 

 substances is also associated with the oxygen eflFect but this question 

 requires special investigations. 



It should be stressed that the efficiency of all the substances tested 

 varies strongly with time. It may be just this fact which accounts for 

 the different data found in the literature. In order properly to evaluate 

 an agent, its efficiency should be tested at different time intervals after 

 injection. 



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