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