X-Ray Sensitivity 



107 



that no additional protection can be afforded by the third 

 chemical because the residual killing effect is the direct damage 

 produced by X-rays on essential components of the cell. 



PER CENT SURViVAL-60 KILOROENTGENS 



18 18 



Fig. 9. Compound graph of additivity tests of: 



Ethyl alcohol plus BAL. 



Ethyl alcohol plus Na2S204. 



Na2S204 plus BAL. 



Ethyl alcohol plus BAL plus Na2S204. 



The figures immediately below and above the names of com- 

 pounds refer to survival obtained for the individual compound. 



Discussion 



It is difficult, on the basis of our meagre knowledge of the 

 mechanism of the effect of ionizing radiation on cell con- 

 stituents, to give a plausible explanation for the protection 

 afforded by this fairly wide variety of compounds against 

 radiation damage. Studies of the effects of X-rays on pure 

 water are of interest in this connection. Many reports indicate 

 the production of radicals like H, OH, HO2, and of HgOg 

 (Allen, 1948; Dale, 1947; Burton, 1947; Stein and Weiss, 1948; 



