irraciated cells to take up tritiated thymidine and thus prepare fbr cell division
under the stimulus.
lus is applied.
This explains the failure of the thyroid to eflarge when the stir
we showed by quan-
In other earlier experiments under these contractgk
itative histochemical measurements of DNA that the nuclei of an ofcasional cell con-
tained much more than two times the diploid value, at which time the cell should have
divided.
We pointed out many years ago when we obtained the first]
biopsies of thyroi
treated with 1 307 and 131; that the large bizarre nuclear forms wilth excessive chromatin resembled neoplastic cells that might have malignant potential.
primary basis for our original AEC Contract).
(This was the
The cummulative evadence increasingly
_ supports the idea that under such conditions those altered cells, Jvyhich can and do
synthesize DNA and occasionally complete the process of mitosis aye the source of
neoplasms.
It does appear that with heavier irradiation the numba
of. cells retainin:
a capacity for mitosis is reduced and thus the chance of a neoplasm
developing is les
We know from previous animal experiments, and suspect from olfervations on clini
subjects, that there is a difference between the effect of a relatfively large dose of
131; which causes both impairment to the synthesis of thyroxine ard
intrinsic nuclear
damage (that precludes subsequent cell division) and the small dose
which damages the
nucleus but does not seriously impair thyroxine production.
The problem has been to
determine these respective doses in the experimental animal.
There is a dose level of 131 I
to the thyroid in man that results in a latent
failure of the thyroid hormone production after all of the isotopq is gone and years
have passed.
(See report by Larson, et al including this author)]
As we pointed
out more than 20 years ago from the work under the earlier AEC contracts, the failure
is attributable to intrinsic nuclear damage which does not destro} the cell nor its
hormone production but does result in ultimate death of the cell When mitosis is
attempted.