13ly radiation. The large bizarre nuclear forms originally fgund and described atne beginning of this project have received in attention. The production of the odd nuclear forms. in animel after only smell doses of 13511 followed by a stimulus of thiouracil has Seen re- ported from this project. The finding of excessively large agounts of DMA as demonetrated by Feulgen staining end quantitative microspeqtrophoto- metry in nuclei of thyroid cells of animals wes reviewed in dat in the complete review submitted two years ago. A manuscript entitled "The Acute and Loi.z Term Effects of Verlous Doses of Radiofodine on the Thyroid of the Rat as Uemonstrated by Mijtotic Activity using Tritiated Thymidine” when submitied to Endocrinol received some relatively minor editorial suggestions which, with the Lovee ox time, re consideration and additional data prospted redesigning the ent presentation. This was retitled"Desoxyribonucleic Acid (DHA) in he Radtated and Stimulated Thyroid". It was resubmitted on January 24, 1957. It hes been accepted and is in press. Copies of this mamiuscript ere ached. Its contents may be briefly reviewed as follows: Tritiated thymidine was used in rats to show rediosutogrephicelly which cells were forming DMA in preparetion for mitosis. Whenian entithyroid drug was added to the drinking water two months after small dose of 1317 was given, there was a much greater rise in the incidenc occurred even though there was no obvious microscopic change y the cells of celle forming DNA than when such a stimulus was applied to ron-racdiated controls. This propensity to over-respond with DNA formation dn stimulation after the 13ly, but before the stimulus was applied. This res occurred long after the 13112 was gone, but while the gland as q stole still had a capacity to enlarge under the antithyroid stimulus. It had_been learmd from the earlier experiments that aficc Fiving a dose of 1311 which was insufficient to produce recognizable sicroscor changes in the thyroid, a latent effect was produced thet rer] resulted in large abnormal nuclear forms when the stimulus of thioureciii wus applied. We also had knowm from earlier experinents that soon #fter an intermediate (5-20 uc) dose of 131zZ (25 to 35% uptake) had been|given, the thyroid could be induced to hypertrophy, as does the normaligiand when an antithyroid as administered. However, several months later and long efter ell the lr had disappeared from the gland, this ) lity of the gland to hypertrophy was gredually lost. [t seemed in the 1 recent experiments that it was among those glands which had received lds rr doses of 1312 and still hed a capacity to enlarge that developed more [o: the abnormal nuclear forms. of It was theese nuclear forms that had exqessive DMA. Qn initial iodine deficient diet had been given to induce a gpod uptake 13lf, ‘this part of the experiment showed how thyroid cells deficient displayed a high degree of DNA synthesis in preparation division. When the fodine deficiency was corrected, DNA syntheals declined. when fodine for cell promptly More attention in the revised manuscript was given to} the observations on DNA synthesis under these conditions of fodine < iency. Nuclear Changes in Human Radiated Thyroid Tissue Over the years there have been opportunities to procure by surgical means, semples of thyroid tissue from patients previously treated with 1511. Having firmly established the method of Feulgen staining end quenitative