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medical and genetic status of the group at appropriate intervals with a view to
learning what if any of the knownlate effects of radiation exposure may be observed. Obviously and indeed fortunately the number of persons [92 Marshallese]
receiving 75 roentgens exposure and greater is too small to make it possible
to determine with any degree of accuracy the effect on life span."
Effects of Radiation Exposure in Humans
The reasonable and superficial evaluation of radiation hazard is that
humans can obviously tolerate exposure to several hundred roentgens, recover
from immediate effects, and remain in ''normal' health and functional capacity.
Recently, however, we have become aware of deleterious long-term effects of
radiation which, however subtle, appear to be proportional to the total quantity
of radiation exposure and may be assumed to act even at very low levels of
irradiation.
Except for these long-term changes, our understanding of radia-
tion effect usually has been concerned with two important facts that dominated
our thinking about these problems:
(a) For certain kinds of radiation damage and injury, there is recovery.
Individuals recover from acute symptoms produced by sublethal radiation exposures even though they may show general sickness, burns, loss of hair,
anemia, étc. Recovery from acute radiation effects is analogous to recovery
from any other acute injury or infectious process in which damaged tissue is
healed and repaired.
(b) These obvious signs of radiation effect are associated with relatively
large single doses of radiation (greater than 100 r). As dose size is decreased,
detectable acute effects decline, becoming disproportionately small, so that
there is a true threshold of dose of irradiation, at about 100 r, below which
these particular acute manifestations of radiation do not occur.
The Proportional-Effect Concept of Irradiation
Recent evidence that long-range effects of radiation simulate aging
effects comes from a variety of sources and is consistent with information
relating radiation effects with genetic change and changes in cell-population
numbers and quality. Evidence and logic support an argument that small
increments of radiation-induced morbidity persist as small permanent changes
in body functional structures, which become detectable as aging, neoplastic
disease, and genetic change (see Appendix A). However, it remains to be
proven experimentally that these effects do occur as the result of small irradiation exposures. The testing of this question is not likely because it would
involve great technical difficulties. Attempts to procure some evaluation of
the problem relating small-dose (5 r to 10 r) effect to life span would involve
study under uniform conditions of perhaps several million mice. It is pointed
out that in order to establish the effect of the smallest doses as yet measured
for genetic effect, namely 25 and 50 r, the geneticist Curt Stern and his associates worked for 6 years and examined approximately 50, 000, 000 individual
flies. They came to the acceptable conclusion that these small exposures
have the same effect per roentgen upon gene mutation as at higher exposures