330 RADIATION STANDARDS, INCLUDING FALLOUT iodine deposition the thyroid aloneis being irradiated—with a minute contribution of total-body irradiation from the radioiodine gamma rays—whereas in the case of thyroid cancer induction following mediastinal irradiation, significant irradiation of many other structures, probably including other endocrine glands, especially the hypophysics occurs at the same time. During the past 3 years no significant body of data has been developed which throwslight on the question of shortening of lifespan following total-body irradiation at low dose rates. Studies will continue and be extended both in this country and abroad on the long-term effects of ionizing radiation on man. This 1s proper and important in spite of the fact that we already know as much or more about the toxicity of ionizing radiations than we do about almost anyother toxic material in our present complex environment. In conclusion, I would like to state my belief that the human studies underway and contemplated will not answer the important questions of linearity and threshold at doses and dose rates near, or a factor of a few higher than, background radiation levels. They may yield some answers concerning specific organ and agesensitivities to ionizing radiation. Large-scale small experimental animal studies will continue to play their role in extending the range of our information concerning linearity and dose-rate dependency in these particular species. In the last analysis, our most important information will come from fundamental studies on the nature of the carcinogenic process. Representative Price. Thank you very much, Dr. Hasterlik. On page 4 youstate that the data of Court Brown andothers do not disprove the Stewart thesis. Why do yousay that? Dr. Hasrertrx. If you will note on page 3, Court Brown and others did the study of those 39,166 children whose mothers were irradiated between 1945 and 1956. The studies on the incidence of leukemia run between 1945 and 1958. A very considerable portion of the children studied had a very short life experience before the study terminated. I don’t remember exactly the numbers, but it seems that something of the order of two-thirds of the children studied were less than 10 years of age at the termination of the study. We do know that some of the cases of leukemia may develop at times later than 1958. SoTI believe that it is too early to say that the data are all in on this study. Besides, the number of cases here, the 9 cases, is very small compared with the expected 10.5. The numbers are small, and the probability of it not being a significant figure exists. J think it is an important study. These prospective studies are very important. J think it tends to help overcomea little of the uneasiness we all felt from the results of the Stewart studies, but Lalso must say it does not disprove Dr. Stewart’s thesis completely. Representative Price. You state that a total of 24 persons develop malignancies out of 300. In your group the lowest terminal body content at which a malignancy was seen was 0.45 microcurie. The pighest was 6.8 microcuries. Are not these above the permissible evel? Dr. Hasrertix. These are certainly above the occupational permissible level for radium. The present occupational permissible level SsneltahgneseshiseetapiscustteaUaoeabatesg3 dees