The danger to the individual as a result of overexposure to high-energy
radiation was understood fairly soon but not before some tragic
experiences were recorded.
One of the early workers with radioactive materials, Pierre Curie,
deliberately exposed a patch of his skin to the action of radioactive
radiations and obtained a serious and slow-healing burn. His wife, Marie
Curie, and their daughter, Irène Joliot-Curie, who spent their lives
working with radioactive materials, both died of leukemia, very possibly
as the result of cumulative exposure to radiation. Other research
workers in the field died of cancer before the full necessity of extreme
caution was understood.
The damage done to human beings by radiation could first be studied on a
large scale among the survivors of the nuclear bombings of Hiroshima and
Nagasaki in 1945. Here marked symptoms of _radiation sickness_ were
observed. This sickness often leads to death, though a slow recovery is
sometimes possible.
In general, high-energy radiation damages the complex molecules within a
cell, interfering with its chemical machinery to the point, in extreme
cases, of killing it. (Thus, cancers, which cannot safely be reached
with the surgeon’s knife, are sometimes exposed to high-energy radiation
in the hope that the cancer cells will be effectively killed in that
manner.)
The delicate structure of the genes and chromosomes is particularly
vulnerable to the impact of high-energy radiation. Chromosomes can be
broken by such radiation and this is the main cause of actual cell
death. A cell that is not killed outright by radiation may nevertheless
be so damaged as to be unable to undergo replication and mitosis.
If a cell is of a type that will not, in the course of nature, undergo
division, the destruction of the mitosis machinery is not in itself
fatal to the organism. A creature like _Drosophila_, which, in its adult
stage, has very few cell divisions going on among the ordinary cells of
its body, can survive radiation doses a hundred times as great as would
suffice to kill a man.
In a human being, however—even in an adult who is no longer experiencing
overall growth—there are many tissues whose cells must undergo division
throughout life. Hair and fingernails grow constantly, as a result of
cell division at their roots. The outer layers of skin are steadily lost
through abrasion and are replaced through constant cell division in the
deeper layers. The same is true of the lining of the mouth, throat,
stomach, and intestines. Too, blood cells are continually breaking up
and must be replaced in vast numbers.
If radiation kills the mechanism of division in only some of these
cells, it is possible that those that remain reasonably intact can
divide and eventually replace or do the work of those that can no longer
divide. In that case, the symptoms of radiation sickness are relatively
mild in the first place and eventually disappear.
Past a certain critical point, when too many cells are made incapable of
division, this is no longer possible. The symptoms, which show up in the
growing tissues particularly (as in the loss of hair, the misshaping or
loss of fingernails, the reddening and hemorrhaging of skin, the
ulceration of the mouth, and the lowering of the blood cell count), grow
steadily more severe and death follows.