Each value in table 1 represents the average of 3 to 8 independent observations. From these experiments it appears that the lag period is appreciably lengthened by as little as 500 ergs per MM2 of ultraviolet, but that doubling this dose results in only a slight further increase for cells grown on solid medium and no increase for cells grown in nutrient broth. The most striking feature of these observations is the marked reduction in the lag period as the result of exposure of irradiated cells to reactivating light. The reactivation treatment appears to have no effect on cultures not previously exposed to ultraviolet light. None of the treatments used affected the generation time during the logarithmic growth period. In all cases this remained at 19 to 20 minutes.

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