same. The integral dose to shielded animals was therefore equivalent to that received by unshielded ones receiving one-half of that dose. Inspection of the data showed a non-linear dose-effect relationship in all cases, with upper convexity. Whole-body exposure was most efficient for induction of life-shorten- ing; shielding of the lower body least efficient; shielding of the upper body was intermediate between the two. The only pathological data given were those referring to overall leukaemia and they are insufficient for any conclusion. Also, the significance of the differences observed between control and treatment groups and between the treatment groups themselves appears dubious. 316. Cosgrove and Upton [C25] exposed RF female mice to 250 kVp x rays, under nembutal anaesthesia and the conditions studied were: irradiation on the wholebody with 100 R or 300 R; 300 R to the upper, middle or lower third of the body; non-irradiated controls. Life~shortening was appreciable after 100 or 300 R given whole-body but survival of the shielded groups was slightly, if at all, different from that of non-irradiated controls. Whole-body irradiation at both exposure levels increased the incidence of thymic lymphoma and in the 300 R group myeloid leukaemia was also increased; but none of the diseases was increased in shielded mice. Since partial exposure of any third of the body to 300 R produced less life-shortening than did 100 R to the whole body, the effect was not correlated with the integral dose. 317. The experiments of Cosgrove, Upton et al. [C20] on LAF1 female and male mice are more concerned with the induction of nephrosclerosis than with lifeshortening, but were performed on partially-shielded animals, showed that shielding of the kidney prevented the induction of glomerulosclerosis and exposure of the kidney alone was as effective as whole-body irradiation for in- duction of this disease. Longevity was reduced by irradiation of the whole- body or by exposure of the lumbar area to 1200 R at 10 weeks of age, but not when the same dose under the same conditions was given at 1 year of age. Par- tial-body exposures below 1200 R gave an insignificant reduction of the mean age at death. 318. Sato, Tsuchihashi and Kawashima [S34] reported that whole-body, head or trunk exposure to 400 R induced significant life-shortening in ddN female mice irradiated when 10 weeks old with 200 kVp x rays. Lower-body exposure to the Same amount of radiation did not result, on the contrary, in any reduction of