obvious changes have been observed (Welander 1959).
However,
Gorbman and James
(1959)
found upon
examining microscopically the thyroids of reef fish
from an area close to a test site that the damage
to the thyroid ranged from zero to 100 per cent.
In those fish in which the thyroid was damaged, the
fish otherwise appeared to be normal.
The cause of
damage to the thyroids was undoubtedly radioisotopes
of iodine,
as internal emitters,
that are present in
relatively great abundance immediately after the
detonation of a nuclear device.
As the half life of
these radioisotopes of iodine is short
hours to 8 days),
(range from 2
the damage to the thyroids would be
expected to occur soon after exposure.
Because the genetic effects of ionizing radiation
occur in the progeny of the exposed individuals and
may be subtle, it cannot be said that mutations have
not occurred in fish in the Bikini-Eniwetok area,
although it can be said that there have been no
recognizable mutations in the thousands of fish that
have been observed.
If mutations have occurred they
are not the type that manifest themselves as morpho-
logical abnormalities.
Laboratory experiments rather
than field observations are needed to determine the
genetic effects of low,
radiation.
(Seymour,
chronic doses of ionizing
1960).
Operation Crossroads during the summer of 1946 provided
the first real opportunity to evaluate the over-all impact of