378 



hadiation hiolocjy 



l)Ut not tor tlic suiriiydiyl compoimds and sodium li_\-di()sid(il('. Sui\i\al 

 ratios lip to .')()() times tliosc of the control aic ohscrxcd witli the optimal 

 concentrations of the various compounds. liAL is rou}i,ldy twice as effi- 

 cient as eysteini', wliicli niny l)e tlic result of its possessing two sulfhydi-yl 

 groups or of the hj^droxyl group also present. Increasing the concentra- 



io--t 



o 



< 

 a: 



o 



> 10— 



> 

 q: 



lo-i 



I 10 



Mg OF OXYGEN /LITER OF SUSPENSION BUFFER 



100 



Fig. 10-5. l"]ffec't of oxygen concentruliou on the survival of bacteria exposed to 

 80,000 V of 250-kvp X rays. (Burnett and Burke, unpublished; see Hollaender and 

 Stapleton, li)53.) 



Table 10-3. Comparison of the Protective Action of Various Groups 

 OF Compounds on Escherichia coli B/r 

 (From Hollaender and Stapleton, 1952.) 



" Ttie concentration of the compound giving a significant increase in survival. 



* The lowest concentration required to give the highest survival achieved under 

 indicated conditions. 



"^ The protection factor is the ratio of X-ray dose required to inactivate a given 

 fraction of cells in the presence of a protective agent to that required in its absence. 



