The development of recovery clones in radiation injured growth cartilage is described and the significance of late degeneration of clones is related to the cell-survival system based on clone counting. Cell-survival data are presented for X irradiations of the cartilage plate in rat tibiae: animals breathing air, D0∼165 rads, n∼6; anoxia, D0∼340 rads, n∼20; animals breathing oxygen at three atmospheres, D0∼145 rads; oxygen at one atmosphere, D0∼150 rads. 95 per cent oxygen and 5 per cent CO2, D0∼150 rads. The variation in recovery ratio with interval between two fractionated doses is described and an unsuccessful attempt made to relate these variations to changes in mitotic index. The results ere compared with survival data from other mammalian cell systems.
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N. F. Kember (1967) studied this question.