Oly. Another set of data that was held to support the notion of non-specific life-span-shortening was that by Lindop and Rotblat [L2]. The main conclusion of this series was that life-shortening was due to a forward displacement in time of all causes of death, without any changes in the relative probability of each cause. It would be of interest to reconsider these data with a more re- fined statistical test [H2] to assess the reliability of the conclusions, particularly since the pathology and the statistics of this experiment were criticized [W1]. It should in any case be pointed out that the authors did recog- nize differences in the relative time of onset of the various diseases between control and irradiated animals: one may wonder therefore how these data could be interpreted, as they were at the time and long thereafter, to support the existence of a non specifie effect of aging. 218. Storer in his 1965 [S20] series noted in the range of between 100 and 500 R of x rays a tendency of the neoplastic diseases to occur earlier in irradiated than in control mice. In the large series of Upton et al. [U7] and Upton, Randolph and Conklin [U9] microscopic pathology was not performed as 4 rule, but the quality of the macroscopic examination of the animals at death was quite good. The authors felt that the death of irradiated animals was cha- racteristically associated with tumoural and degenerative diseases of the old age, but that neoplastic conditions could not entirely account for the reduction of life. When some of these data were reassessed by Walburg [W1] with more re- fined statistics, the life-shortening in the irradiated mice was negligible when the tumour deaths were excluded. This indicates that tumours did contribute sub- stantially to life-shortening, at least in the dose range of 100 to 300 rad of gamma rays. Similarly, Darden et al. [D1] and Walburg [W1] ascribed to thymic and myeloid leukaemia most of the mortality increase observed in RF mice irradiated, respectively, with neutrons and with x rays. 219. Grahn, Fry and Lea [G5] ascribed to excess tumour mortality the life- shortening observed up to about 400 rad, while at higher doses the decreased life expectancy was not accompanied by a parallel increase of tumour incidence. Maisin et al. below the LD [M10] on Balb/c and C57BL mice attributed life-shortening at doses 50/30 merulosclerosis. essentially to thymic lymphoma and, at higher doses, to gloSimilarly, malignant tumours at the low doses and glomerulo- sclerosis at high doses were identified by Metalli et al. ses of premature death in irradiated mice. [M9] as the main cau-