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The observation of recovery of living cells from the effect of ionizing radiations has been reported repeatedly. The literature concerning this effect has been reviewed by Lea ('47) and more recently by Gray ('52) and Allen et al. ('51). Revera1 techniques have been employed to demonstrate recovery in living organisms, eg., comparison of the efficiency of single and fractionated doses of a radiation or comparison of the efficiency of a radiation applied at high and low intensities. Tlie use of these techniques has yielded information coiicerning the recovery which occurs during the course of radiation exposure. A review of the literature (Lea, '47) indicates that bacteria irradiated in aqueous suspensions do not recover during the exposure to ionizing radiations. Some types of cells a r e able to recover from the effects of ionizing radiations if maintained in the cold or in a starved condition after irradiation (Strangeways and Fell, '27 ; Spear and Gliicksmann, '39; Cook, '39; Allen et al., '51). I n some of the cases reported, however, apparent recovery was in fact merely a postponement of the radiation effect, which was shown to take its normal course when active metabolism and growth were resumed. Latarjet ('43) showed that holding bacterial cells on nutrient agar a t refrigerator temperatures

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