subtle functional aypairmen i t, was present for ls years following doses of 50, and 100 ne of 131] to animals. It was discovered in these studies that] thyroids failed to enlarge in response to the administration of thiouracil spite of the increase in cell height. The bizarre nuclear forms became ap after the administration of the thiouracil. Such changes were produced in that had received 5 pic and were accentuated in animals that had received 2 100 pe. The results of these studies were published. 20, the Maloof, F., Dobyns, B.M., and Vickery, A.L.: The Effects of Various Doses Radioactive Iodine on the Function and Structure of the Thyroid of the Rat. Endocrinol. 50: 612-638, June, 1952. Morphulogical Changes in the Nucleus of Rat Thyroids Following131 Radiati One of the primary objectives from very early in this contract has the nature of the large irregular hyperchromatic nuclei in irradiated numbers of rats were placed on an iodine deficient diet for a mumber of da to study . Large and then given various single doses of 131] to study muclear changes in a variety o ways. previously observed, changes appeared in several months and were accentuat administration of thiouracil. The impairment to the glandular enlargement usually produced by the administration of thiouracil, was again evident fo of isl, which were not large enough to cause architectural distortion. By frequent observations it became evident that the impairment to enlargement in the mildly irradiated gland surprisingly did not occur promptly after 1 been given but occurred after a considerable lapse of time, long after the vanished from the gland. See attached Figure 5. The appearance of abuncs nuclear forms and the inability of the gland to enlarge on thiouracil se temporally related. These opservations supported our belief that the irre forms represented preparation for but thwarted attempts at cell division. of hypertrophy was suspected to be a consequerce. In order to explore this possibility, animals were divided into sev depending on the radiation which they had received and were given colchici attempt was made to determine a mitotic index in the previously irradiated animals treated in various ways with thiouracil and colchicine. Unfortuna mitoses seemed to be either sufficiently infrequent or unidentifiable so experiments did not yield conclusive results as to the frequency of mitose more extensive studies of nuclear change will be described. AS by the tis i doses ing more f the gland T_ had Sly had bizarre to be nuclear failure - groups An ids of y the +t these Other Observations on the Biochemical Changes Resulting from a Single Therapeutic Dose of 4917 in Man Early in this project enormous amounts of time were devoted to collect detailed data, especially kinetic data, on selected patients who were give therapy for hyperthyroidism. Only selected patients could be used because enormous amount of time required for the study of a single patient. The s clinical effects of 131y therapy have been ultimately measured against a background of data on each individual patient. It was hoped that in this might be possible to find explanations for the great variation in the re different patients to this therapy. The responsible investigator is in 131+ therapy, as well as other forms of therapy for hyperthyroidism at Cle Metropolitan General Hospital. There has thus been an opportunity to stud patient in great detail and to organize all studies in a predetermined fa the largest amount of information could be obtained from each patient, whe treated surgically or with 131, .