changes might have appeared in the thyroid if these patients had survived. However, the evidence from other studies strongly indicate that if any “pathological effects were to be noted in the thyroid after an exposure of pome 10,000 reps they would be minimal. Likewise, the possibility of serious damage to other organs of the body, such as parathyroids and trachea which are simultaneously exposed to the yi31 radiations, would be exceedingly small. On long term effects, two summarizing statements may be made. "No thyroid neoplasm was found which could be attributed to piston 26 after doses to normal thyroids running into many tens of thousands of reps and after periods of observation up to more than eight hundred days. "In a series of over 400 patients treated with radioactive iodine at the Massachusetts General Hospital during the past ten years no known carcinoma of the thyroid attributable to this agent has developed. Definite answers to the question of carcinom formation mist await prolonged observation of treated patients." 23 Here the average treatment dose of r31 was 10 millicuries and of 73° 25 millicuries. However, significantly lesser doses may be carcinogenic in children.@! "It has been suggested thet the human thyroid is less radiosensitive than other tissues, such as bone, since after many years of treatment of Graves’ disease with radioactive iodine, no cases of resulting carcinom have been reported. The customary dosages of r31 in such cases yield at least 4000 rep to the gland. On the other hand, carcinoma of the thyroid found in children and young adults has almost invariably been preceded by x-ray treatment to the upper part of the body, in amounts such as to yield as little as 200 r to the infant thyroid. It has been estimated that less than 3% of such DOE ARCHIVES