the life-span. posure. Per volume dose, life-shortening was maximum for the head ex- Gompertzian plots of all groups were linear, but they did not bear any simple relationship between partial- or whole-body irradiation. 319. In other experiments conducted on ddN female mice (10 weeks of age) by the same group of workers [$43] the effects of 600 R given whole-body or of 800 R given only to the head, the trunk or the lower body were compared. The mean survival times and per cent life-span-shortening observed in the various groups were as follows: control: 69.2 weeks; whole-body exposure: 43.0 weeks 6 per cent/ 100 R; exposure of the trunk: 59.7 weeks, 2 per cent/100 R; lower body exposure: 62.7 weeks, 1 per cent/100 R; head exposure: 66.1 weeks. The life-shortening effects observed in the irradiated groups were all significant, except for the group with head exposure. The increase in incidence of all tumours and of mali- gnant lymphoma was significant in the whole-body exposed group. Head exposure enhanced the induction of tumours of the pituitary gland; trunk exposure that of ovarian tumours (with a depression of malignant lymphomas); lower body exposure gave the same tumour spectrum as the control. Judging by the mean after-survival of mice dying for the same cause, an earlier appearance of all causes of death (and particularly of the lymphoma) in irradiated than in control groups was apparent. The larger life-shortening produced by the whole-body treatment was attributed to the high incidence of lymphoma and to the arly appearance of lymphomas, lung and mammary tumours. The lower incidence of lymphoma in the par- tially-shielded mice was responsible for the low life-shortening efficiency of these treatments. 2. Rat 320. In the rat Maisin et al, [M23] and Dunjic et al. [D7] performed a study of the mean duration of life of a homozygous strain exposed under various conditions. They found that 600 R given whole-body gave a reduction of life-span of about 41 per cent; 850 - 1000 R to the abdomen alone reduced the life-span by 18-34 per cent. There were also groups irradiated over the thorax only (600 - 3000 R) or over the head only (600 - 2000 R). The survival curves had distinctly different shapes depending on the region of the body exposed and on the various modes of death showing at characteristic doses: pulmonary and oesophageal syndromes for thorax irradiation and delayed head or oropharingeal syndromes for irradiation of the head. The authors suggested that the survival curve after whole-body irradiation could be a composite of the survival curves