Immediate and Delayed Effects of Radium (Gamma Rays) on Tissue Culturesin Vitro

(i) The number of cells in mitosis in tissue cultures in vitro was found to increase up to a maximum which was maintained for a period of approximately 20 hours. (ii) Exposure of tissue cultures in vitro to gamma rays of radium produced a fall in the number of cells in mitosis. (iii) Under certain conditions the fall was followed by a rise which was almost exactly compensatory. (iv) A delayed lethal effect followed prolonged exposure to gamma rays, the average period of survival varying with the duration of exposure. (v) The effect of gamma rays on mitosis and on the survival period after prolonged irradiation, was more marked with 300 mg. radium than with 100 mg., alteration in the duration of exposure being made so as to give a constant value to the product of time and intensity.