oho. A more refined analysis of the above data [Gh] allowed the conclusion that all genotypes exhibited a radiation induced life-shortening effect depending on a single common primary injury parameter. For acute single-dose exposures the parameter could be expressed by the number of days of life lost/ unit dose, equalling 0.28 days/R. This parameter could be combined with others to give equations predicting the life-shortening for any combination of normal life expectancy, dose, incidence of neoplastic conditions. After correction for leukaemia and ovarian tumour induction, life-shortening for both sexes following exposure to 570 R was 111 days and exposure to the same LD @ constant proportion of life lost amounting to 19 per cent. caused In aoretion-of- life experiments mean survival time and mean accumulated dose varied directly with control survival and therefore at each exposure-rate strains having different control survival lost the same proportion of their life expectancy. With a few exceptions, the mean accumulated dose and the acute LD 50/30 were shown to be correlated to each other in that each had a common relationship to the normal life-span. aut. Gowen and Stadler [G11] published also a large series of experiments where ten different mouse strains (four pairs for each genotype) were initially exposed from mating to death to 6005 gamma-irradiation (0.6 to 2.7 R/ day) for 22 hours/day. The design and the analysis of this research, although involving irradiation for the duration-of-life, was centered more on the capacity of irradiation to stop the reproductive functions of these mice, than to shorten their life-span. eke. Other analysis by the Argonne group [S5, G9] contain comparisons of the relative life-shortening effect of °C irradiation to death in genetically dif- ferent mouse strains and indicate the constancy of the slope of the relationship expressing the log mean after-survival against exposure-rate. The linearity of this relationship over the exposure rate range between zero and 56 R/day was es- tablished for BCF1, C57BL/6, Balb/c and A/Jax male and female mice [S5], thus confirming previous findings with the LAF1 mouse [S84]. The control survival of the male and female mice of the four genotypes cited (8 groups in total) ranged from 466 to 796 days and these differences in life-span curves were nearly parallel and were displaced from one another by the same amount of displacement of the control survival times.