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Significant increases in rate of mitosis were found to follow treatment of yeast cells with acute doses of either x rays (500 r) or ultraviolet light (200 ergs/mm/sup 2/). Mean generation time was decreased by as much as 14% over a period of three generations. The stimulation was detected in the generations after the second post-irradiation division of cells. From the observations it was concluded that the increase in mitotic activity is an effect of the radiation on the cells and is not due to changes in the irradiated medium. The stimulus is transmitted to successive cells but is not a result of mutation. There is a correlation between length of inhibitory period and degree of later stimulation. However, results of tests suggest that the inhibition does not bear a causal relationship to the stimulus; cells are stimulated when inhibitory influences are absent. (auth)
James et al. (Thu,) studied this question.