DISCUSSION 257 



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DISCUSSION 

 Rubin: 



I should like to discuss briefly the radiation deaths in various strains of E. coli. 

 It has been shown that the B strain, the parent strain, and the B/r, which is 

 derived from the B strain, show different sensitivities to ionizing radiation. It 

 has further been shown that B/r resembles K12 and most other strains of E. coli. 

 In other words, the B strain tends to be the one that stands by itself rather than 

 the B/r strain. If one examines the data, it would appear to be evident that two 

 different mechanisms of killing both apply to the B strain and only one mecha- 

 nism of killing to the B/r strain and to the K12 strain. It may be that the reason 

 that Latarjet has not found reactivation is that in one strain a certain mechanism 

 is operating and in the other strain another mechanism is operating, so one would 

 not expect to find comparable results in his two strains. 



Latarjet : 



I am very much interested in this remark. As a matter of fact, K12 is signifi- 

 cantly more resistant to radiation than B, though still more sensitive than B/r. 

 Therefore, B/r should be tested for catalase reactivation. However, there might 

 remain some differences between K12 and B/r, such as recombination, which 

 could account for differences in beha\aor regarding the catalase phenomenon. 



Dale : 



I am very interested in the fact that the results varied with the presence or ab- 

 sence of oxygen in these experiments. I should like to ask Latarjet whether in 

 his quinhydrone experiment the control without radiation in the presence of 

 oxygen showed a change to the oxidized form. 



Latarjet : 

 No. 



