STUDIES ON CELLULAR BASIS OF RADIATION LETHALITY .2. SURVIVAL-CURVE PARAMETERS FOR STANDARDIZED PLANARIAN POPULATIONS

The planarian lends itself to the study of the cellular basis of radiation lethality because it contains a single, morphologically identifiable, population of totipotential stem cells, without which the animal cannot long survive. The effects of pre- and post-irradiation decapitation, age (sexual maturity), and hypoxic irradiation conditions are examined to determine further those conditions for which radiation lethality is most likely to be determined solely by the degree of depopulation of reproductively intact stem cells. Under such conditions, whole-animal survival parameters have been determined for each of the five species and polyploid biotypes studied. Radiation lethality was not affected by decapitation or by age, but oxygen enhancement ratios of 2·5 to 3·4 were obtained. At the level of the whole animal, polyploidy gives no protection against radiation. Species differences are at least as great as generic differences in radiosensitivity. © 1968 Informa UK Ltd All rights reserved: reproduction in whole or part not permitted.