Abstract
Radioresistant cultures of the L5178Y leukemia were obtained during continuous β-irradiation at 4.8 rads/hour by means of tritiated water incorporated in the culture medium. The development of radiation resistance in individual cultures after exposures of 39 days or more (total dose ≥ 4.6 krads) was shown to be due to the production of resistant mutants during the course of irradiation. In the resistant cell strains derived from the mutants the chromosome count was unchanged from the modal value of 40, and the ability to grow in the DBA/2 mouse was unchanged. In the absence of radiation, resistant cultures grew rather more slowly than normal cells. Under continuous irradiation the mutants differed from each other in growth rate and in the proportion of dead cells present. The resistant cell strains were maintained at 4.8 rads/hour for nearly a year, during which the growth rate of the less resistant cultures speeded up in steps corresponding to the occurrence of further mutations, eventually reaching abou...
Published Version
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