series the effect dose, dose rate, age at exposure and genetic background on a . oo . variety of late effects, including life-shortening, by 60 - Co gamma rays in mice. It is proposed that the present Annex should include a review of these data as soon as they will become available in a more complete form. 2. 81. Rat There are a few data on single-dose irradiation of rats. Hursh et al.[H5] irradiated Wistar male and female animals with 250 kVp x rays in the range of 150 to 600 R. They found a decrease of the survival time proportional roughly to exposure, the per cent reduction of life span/100 R being between 4.2 and 4.9 for male and between 2.8 and 4.0 for female animals. Inspection of the data shows an approximate linearity of the experimental points, although the error is fairly large, since the various dose groups included a maximum of 24 animals each. 82. Wistar females surviving an acute whole-body exposure to hypoxic irradi- ation (250 kV x rays, 1000 R) showed some life-shortening compared to controls. Tumours appeared sooner in the irradiated animals but their final incidence was not increased. This early onset of neoplasia was best explained as one aspect of the accelerated aging process, although other diseases prevalent in old rats (cataract, acute inflammations, epilation, skin ulcerations) were also accelerated to a comparable degree [L3]. these animals and increased blood pressure Nephrosclerosis in 46 per cent of (the two conditions being rather unrelated) were reported as pathological findings in another paper by the same group [L5]. 83. Again in the rat (female Long-Evans-Wistar hybrid) life-span-shortening was observed after acute whole-body x ray exposures (250 kVp at 55 R/min.) of 120, 240 and 480 R. Under these conditions the efficiency of the treatment / rad was found to vary from 0.60 to 0.76 to 0.52, respectively, at the abovementioned doses [L4]. 3. Bh. Guinea—pi In experiments by Kimeldorf, Phillips and Jones [K8, K9] young adult male guinea-pig from a SPF Hartley colony were exposed to a simulated fission spectrum