«~ § = and how many cells possessed nuclei that were preparing for mitosis. some instances the rats were also given minute trace doses of 131f to test the function of the thyroid before they were sacrificed. The In radio- autographs: for tritiated thymidine were not prepared until the 1f1r had completely decayed. Some animals were killed early in the courselof the experiments to gather additional data on the supramaximal surge of DNA formation that had been observed in previous experiments two months after the 131] was given. Body weights, thyroid weights and thyroid fusction, as measured by 131r uptake, as well as grcss changes in thyroids,|are all being determined at the time of sacrifice. The longest of these experiments hare been in progress for about 1* years, Intervals thus far selected for sacrifice have been 34 mouths, . 9 months, 1 year and 1% years. They will be sacrificed at 2 year$ end 2% years. It is hoped that the intervals elected for sacrifice give radioautographs at the time when the first signs of the developmest of neoplasms occur. ne ine reprlammebegin to develop. it is anticigated that clusters of cells which repre sent incipient tumors aene displ different proclivity for synthesizing DMA. At the time of the pro= gress report no gross tumors had appeared in animals that had bee sacrificed. At the end of one year5 sacrificed animals showed some gqul axi- ties in the thyroid. Ra hse were not as good as they shquld have been for interveetation of teitsum in nuclear DNA. New radicautogrepl have just been completed and srenot particular arly revealirg, probably be—cause the nodular areas are not sufficiently distinct. Tissues oljtainec at 18 months show 4 examples of more irregularity in each series. autographs are in preparetion on these tissues. Radio-= It is interesting that the irregularities sre developing in the gland a little more feq mtly in the animals given 131r alone than in Lily plus chronic aduinistratlion of azcithyroid drug. It now seens apparent that there should be a thir series of animals thet are such younger than either of these two deries when 131r is given, i.e., weanling rats. Chromosome Abnomalities in Circulating Leukocytes of Patients ated with Several years ago we solicited the assistance of Professor Ne Macintyre of this University in the study of chromosomal anomalies in circulating white ceils in a patient treated with large doses of e+I. In our comprehensive review two years ago, we described our observations the very high incidence of chromosomal anomalies in a patribnt whom we had given several very large doses of 13511 end had died in to great detail. These observations were published several yeats agofas the first American publication of its kind, In those studies we found] that a high incidence of anomalies Gk years after the last of a total of +75 millicuries of 1312, With the very extensive experience in chros preparation am interpretation by Dr. Macintyre and his associates ‘it seemed appropriate to carry these observations futher and look for] anomalies in individualswho had received doses of 8 to 15 millicuries of 131f as of 8 to 12, sxples of blood during a two week period following a tteatment treatment for hyperthyroidism. In the meantime observations have beer reported by others who have used one or two observations on each of several patients rather than a series of cbservations on each patient to prove unquestionably that a change had taken place and to observe a sequence of changes, It has been ow policy to make multiple cultures from a §eries aaan a