X-Ray Sensitivity 



105 



protection (Fig. 8). The possible mechanism is a depletion 

 of oxygen from the suspension by the bacterial cells in the 

 presence of an oxidizable substrate (Stapleton, Billen, and 

 Hollaender, 1951). 



< 

 a 



> 



•o-i" 



f^^ 



t 



10 



-4 



Hi 1 



BUFFER 

 CONTROL 



^1 



-> — r- 



\0' 



T 1 1 < 1 1 1 



I0-' 10-2 



MOLAR CONCENTRATION 



NAjSjO^ 



10-* 



-T — i 



1.0 



Fig. 7. Survival of E. coli in different concentrations of sodium 

 hydrosulphite at 2^0,. (60,000 r). Morse, Burnett, Burke and 



Hollaender (in preparation). 



The survival curves beginning with 15,000 r are linear over 

 the entire range studied. At lower energy values for aerobi- 

 cally grown bacteria irradiated anaerobically and for bacteria 

 grown in the presence of protecting chemicals the survival 

 curves may appear to be sigmoid in shape. Unfortunately 

 this is a region where it is not simple to obtain highly reliable 

 values. Such data are not available at the present time. In 



