of resistant colonies to bacteria sprayed. Thus, 

 crowding cannot account for the lower colony counts 

 from unspread plates. 



This experiment, therefore, confirms the conclusion 

 drawn from the fluctuation test, namely, that phage- 

 resistant variants arise by spontaneous change prior 

 to contact with phage. 



Howard B. Newcombe 

 Atomic Energy Project, 

 National Research Council (Canada), 



Chalk River, Ontario. Jan. 7. 

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