The Effect of Variations in the Dose-rate of Gamma Radiation on Cell Degeneration in the Frog Tadpole

(1) Tadpoles were exposed to a dose of 336 r of γ radiation, given at five different dose-rates varying from 5 to 20 r/min. (2) The effects, measured by the number of mitotic and degenerate cells present at different intervals after exposure in the brain and the eye, varied with the dose-rate as follows:— (a) The maximal degeneration count increased with the dose-rate. (b) The interval between irradiation and the time at which degeneration reached its maximum increased with the dose rate. (c) The total amount of degeneration was highest for a dose-rate of 15 r/min. (3) The results show that under the conditions of these experiments there is an optimal dose-rate. (4) The experimental results are discussed in terms of the interaction of the various biological processes involved.