the animal sex were not found to influence the extent of this life-shortening. In dogs, rabbits and monkeys which were irradiated for only a fraction of the life-span no effect on survival times was found at exposure rates below 1 R/day. Boche's contribution emphasized particularly the importance of the net increase in mortality rate/roentgen in characterizing the relative species sensitivity. 107. In the experiments of Lorenz et al. [L6] (reported also by Lorenz [L8] in a less complete form) C3Hb female and LAF? male and female mice were given life-span exposures of 0.11 - 8.9 R/8-hour day of gamma-radiation. There was a@ progressive decrease of the mean survival time with increasing daily dose. At the 4.4 and 8.8 R/day level there was an early acceleration of the death rate, which showed later (at around 20 and 24 months after the beginning of exposure) also in the 2.2 and 1.1 R group and was taken to be a manifestation of the cumulative character of the radiation injury. By plotting mean accumu- lated dose versus mean survival time a straight line was found to represent the data adequately over the dose interval considered. No predominant cause of death was apparent. 108, In the case of guinea-pigs exposed under similar conditions the death rate was greatly accelerated already at the 4.4. and also at the 2.2 R level, by comparison with the mice, showing that bone-marrow failure was killing the guinea-pigs at short terms. Survivors at 1.1 R/day had a shorter life-span. In this species the curve describing the mean survival time as a function of the mean accumulated dose, after an approximately linear relationship of the two variable up to 4.4 R/day was shown to bend back sharply because of the appearance of the early syndrome of pancytopenia. 109. The mouse data in the experiments by Lorenz et al. by Failla and McClement [L6] were reanalysed [F4] by the use of the Gompertz function, in such a way that the resulting curves might be internally consistent. The straight slope of the Gompertz plot (see Figure I) was taken to represent the effect of the aging process, whatever its mechanism might be. Chronically-irradiated mice had a steeper slope which phenomenon, on the above assumption, would be taken as an acceleration of aging. From the relative position of the Gom- pertz-lines a fictitious dose rate of radiation was calculated (amounting to 12.8 R/day) that would cause the same aging as occurred spontaneously. This analysis was used as a preliminary step to infer life-span-shortening valuesapplicable in the human species.