The present experiments have shown a high correlation (<tex-math>$\rho ^{s}=0.97$</tex-math>) between the survival of irradiated E. coli B and the viability of nonirradiated E. coli B, plated on various media at various temperatures. The degree of the effect of the media after irradiation with doses of 20 kR can be ten- to twentyfold. The dependence of the survival of irradiated bacteria on postirradiation conditions is well known and is usually interpreted as a recovery effect. The data obtained by us indicate that variation in the levels of survival of irradiated cells may be due to a selective effect of the medium. To distinguish between these two hypotheses, additional investigations are required.

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