29h. Paradoxical effects induced by relatively low doses of radiation which increased, rather than decreased, the expectation of life are not uncommon in the papers reviewed. In addition to the experiments just cited on the rat [c21, C22], observations on mice by Lorenz and co-workers [L6] are to be mentioned. Here, mice exposed throughout life to 0.11 R of gamma rays daily had an increased after-survival with respect to controls. This increase was not statistically significant, but was confirmed in a subsequent test. There were differences between groups concerning the air conditioning and temperature of the animal quarters which made the data uncertain. No reduction of the mean after-survival of three different strains of mice exposed to 5 R/day and to cumulative exposures of about 2500 R was observed by Sacher and Grahn (cited by Sacher and Trucco [S32]. Yuhas [Y3] also reported life-span lengthening when old animals (15, 18 and 24 months old) were exposed to 10 fractions of 140 R of x rays given over 12 days, wheras the same amount of radiation admini- stered to 4 or 9 months old animals produced some life-shortening. It should also be recalled that life-lengthening in animals irradiated in their old age is by no means a strange finding [K6] (see paragraphs 262-280). 295. Following the formulation of a theory on the statistical nature of mor- tality by Sacher [S2] and by Sacher and Trucco [812] in which the death of an organism is viewed as a random event arising from the fluctuating nature of its physiological performance, these two authors proposed [S532] a modification of the theory that makes it possible to account for paradoxical observations of the type described. Radiation (particularly at low doses) would induce a decreased fluctuation of the signalling and control systems of physiological processes. As a result, the probability of a large fluctuation leading to an irreversible change would also be decreased. In essence, the decreased vari- ability among the exposed than among the control animals would be the main effect of the irradiation and the improved survival at relatively low doses would result from it as an occasional consequence. 296. In experiment by Gambino et al. [G13] Long-Evans female rats were irra- diated over the whole-body or only on the adrenals with 500 R and then exposed for three hours daily to o°C. Reduced longevity was among the effects (re- tarded growth, cataract, fur graying tumours) seen at long-term in the whole- ‘pody-irradiated (but not in the adrenal-irradiated) rats. It amounted to about 20 per cent of the normal control life-span and it was not modified by the