Another difference between the genetic and somatic effects of radiation
rests in the response to changes in the rate at which radiation is
absorbed. It makes a considerable difference to the body whether a large
dose of radiation is absorbed over the space of a few minutes or a few
years.
When a large dose is absorbed over a short interval of time, so many of
the growing tissues lose the capacity for cell division that death may
follow. If the same dose is delivered over years, only a small bit of
radiation is absorbed on any given day and only small proportions of
growing cells lose the capacity for division at any one time. The
unaffected cells will continually make up for this and will replace the
affected ones. The body is, so to speak, continually repairing the
radiation damage and no serious symptoms will develop.
Then, too, if a moderate dose is delivered, the body may show visible
symptoms of radiation sickness but can recover. It will then be capable
of withstanding another moderate dose, and so on.
The situation is quite different with respect to the genetic effects, at
least as far as experiments with _Drosophila_ and bacteria seem to show.
Even the smallest doses will produce a few mutations in the chromosomes
of those cells in the gonads that eventually develop into sex cells. The
affected gonad cells will continue to produce sex cells with those
mutations for the rest of the life of the organism. Every tiny bit of
radiation adds to the number of mutated sex cells being constantly
produced. There is no recovery, because the sex cells, after formation,
do not work in cooperation, and affected cells are not replaced by those
that are unaffected.
This means (judging by the experiments on lower creatures) that what
counts, where genetic damage is in question, is not the rate at which
radiation is absorbed but the total sum of radiation. Every exposure an
organism experiences, however small, adds its bit of damage.
Accepting this hard view, it would seem important to make every effort
to minimize radiation exposure for the population generally.
Since most of the man-made increase in background radiation is the
result of the use of X rays in medical diagnosis and therapy, many
geneticists are looking at this with suspicion and concern. No one
suggests that their use be abandoned, for certainly such techniques are
important in the saving of life and the mitigation of suffering. Still,
X rays ought not to be used lightly, or routinely as a matter of course.
It might seem that X rays applied to the jaw or the chest would not
affect the gonads, and this might be so if all the X rays could indeed
be confined to the portion of the body at which they are aimed.
Unfortunately, X rays do not uniformly travel a straight line in passing
through matter. They are scattered to a certain extent; if a stream of X
rays passes through the body anywhere, or even through objects near the
body, some X rays will be scattered through the gonads.
It is for this reason that some geneticists suggest that the history of
exposure to X rays be kept carefully for each person. A decision on a
new exposure would then be determined not only by the current situation
but by the individual’s past history.
Such considerations were also an important part of the driving force
behind the movement to end atmospheric testing of nuclear bombs. While
the total addition to the background radiation resulting from such tests
is small, the prospect of continued accumulation is unpleasant.
What’s more, whereas X rays used in diagnosis and therapy have a humane
purpose and chiefly affect the patient who hopes to be helped in the
process, nuclear fallout affects all of humanity without distinction and
seems, to many people, to have as its end only the promise of a totally
destructive nuclear war.
It is not to be expected that the large majority of humanity that makes
up the populations outside the United States, Great Britain, France,
China, and the Soviet Union can be expected to accept stoically the risk
of even limited quantities of genetic damage, out of any feeling of
loyalty to nations not their own. Even within the populations of the
three major nuclear powers there are strong feelings that the possible
benefits of nuclear testing do not balance the certain dangers.
Public opinion throughout the world is a key factor, then, in enforcing
the Nuclear Test Ban Treaty, signed by the governments of the United
States, Great Britain, and the Soviet Union on October 10, 1963.