with the dose scales in the ratio of 1 to 13 (see figure XIV). The agreement of the experimental series was, at least for the mouse, surprisingly good and exposure levels of 10 R/week or higher of gamma rays shortened the mouse life in a reproducible manner. There were eight experimental estimates at weekly doses of less than 10 R/week (or its neutron equivalent) and in none of them the duration of life was significantly different from the respective control value. Taken at face value, these data suggested therefore an apparent thres- hold at dose rates below 10 R/week or its neutron equivalents. 114. Moos et al. [M14] and Yusken et al. [Z2] carried out experiments on CFW mice of both sexes, individually caged and irradiated with 400 kVp x rays at daily dosages of 2 - 512 R. The survival time of the mice descreased as the daily dose increased but the decline was not very rapid up to 8 R/day. Expo- sure of up to 4 R/day allowed the animals to accumulate 600 - 1400 R before one-half of the mice died. 16 or 32 R/day. About 2900 R of accumulated radiation was given at In a subsequent paper Moos [M15| tested the possible exis- tence of a threshold in the same mice. He showed that variability of the con- trol population and of the animals receiving 2 R/day was the same or could not be resolved statistically and concluded for a continuous effect of life-span reduction down to the smallest dose rates tested. 115. Of particular interest to the problem of life-time irradiation are the data by Sacher and Grahn [S4] on more than five thousand LAF1 male and female mice given 604, gamma ray exposure starting from the age of 100 days. These data represent up to the present the most complete and exhaustive experimental series on this subject. The exposure levels used were 36, ranging from 5 to 200.000 R/day and corresponding mean survival times from about 500 days to 6 hours. The daily doses between 5 and 2500 R (giving mean after survival times of 5 or more days) were delivered during 12 or 15 hours/day; higher daily doses were given almost continuously. Dosimetry was particularly accurate and fully discussed. 116, Survival data were analysed by an empirical function of survival time and dose-rate, the cumulant lethality function, co (te) % = $0 7 — Che -#) t* -_— ° defined as (15) 1