in fact proposed, of which the majority were obtained from gamma-ray chronic
irradiation data (see Table 3).
Most of these data agree in showing that the
rat, the dog and the mouse are about equally sensitive, while (on the basis of
very scanty data) the rabbit would appear to be less susceptible and the monkey,
the goat and the guinea-pig perhaps more sensitive.
As to the man, its sus-
ceptibility is reported in one case to be higher (perhaps by a factor of two)
and in another case to be similar to that of dog and the mouse.
It does not
appear from the data that the differences between the various mammalian species
testedis very large and the range within which all species might be included
could possibly be a factor of two in both directions (taking the mouse and the
dog to be in the middle of an ideal radiosusceptibility scale) or about a factor of five over the whole range of radiosensitivity of the species tested.
283.
Intra-species or inter-strain variability has also been studied in the
mouse, the species where different genetically-homogeneous strains are more
easily available.
When adequately looked for, differences between various
strains (for the same sex) were easily observed.
No formal genetic analysis of
the radiosensitivity parameters has been attempted and most of the data refer
to irradiation for’ the duration-of-life.
In general the amount of life-shor-
tening is correlated with the control mean survival time, in the sense that the
proportion of life lost per unit dose is similar for the various strains having
different life-spans.
Life-shortening is also correlated with the expression of
the pathological characteristics of the strains, since animals prone to the development of leukaemia and of ovarian tumours (the cases more thouroughly an-
alyzed) show a greater amount of life-shortening per unit dose.
It is possible
that the differences in response of the various strains may also reflect the
maturation rate of the genotypes irradiated, as some data on the correlation of
the response with the weight of maturing animals would suggest.
When allowance
is made for all these variables the mouse appears to respond according to a baSic parameter, whereby for acute single doses the number of days lost per unit
exposure equals 0.28 days/R.
On this basic dose-response relationship all the
factors mentioned above (in addition to other factors for sex and age) would
superimpose to give the compounded final value of effect applying to each particular situation.
28h.
In few of the data reported either no difference or small differences in
sensitivity to life-shortening were reported between male and female animals: