114 LARSENetal. radiation alone seldom develop hypothyroidism. However, there are two populations of patients who may develop hypothyroidism following external radiation therapy: those with head and neck tumours who received radiation therapy following surgical manipulation, and those with malignant lymphoma treated with radiation therapy after lymphoangiography. Since hypothyroidism is usually associated with high doses of radiation to the thyroid, how do you account for your findings with low doses? R.A. CONARD: In our studies we are using very sensitive tests for thyroid function, and our findings indicate only biochemical or subclinical hypothyroidism at present. If these sensitive tests were used in other cases following external irradiation, perhaps such effects might be demonstrable. Y. NISHIWAKI: I also conducted an analysis in Japan of the highly radioactive fall-out on the Japanese fishing boat that was engagedin fishing about 80—90 miles east of Bikini at the time of the thermonuclear test conducted early in the morning of 1 March 1954, and which returned to Japan in the middle of the same month. According to the statements of some of the crew, a few hours after the thermonuclear detonation in Bikini the whitish dust began to fall on the boat so heavily that for a period they could hardly bear to open their eyes and mouths. It continued to fall for several hours. Some of the crew apparently tasted it, to see what it was, without knowing that it was highly radioactive. Owing to the difficulty of dose estimation without more accurate information on theinitial condition, the radioactive fall-out conditions on the boat were experimentally reproduced by M. Miyoshi, the chief physician in charge of treatment of the exposed crew at the Tokyo University Hospital, using pulverized coral reef. This experiment was carried out in the presence of the crew as witnesses of the actual amount of ash which had fallen on the boat. This amount was then estimated to be about 3.38—8.52 mg/cm?. Theradioactivity of the ash was estimated by extrapolation to be about 1 Ci/g at the time it fell on the boat. Taking into consideration various possible exposure conditions of the crew during the voyage, the probable gamma dose wasestimated to be in the range 170—600 rad. The degree of uncertainty was far greater for the internal dose. The long-lived radionuclides detected in organs such as theliver many weekslater could not be considered the only sources of internal exposure. Depending on the assumed degree of initial incorporation of short-lived radionuclides, a wide range of estimates was possible: for the liver, a few rads toa few tens of thousandsof rads, the probable dose range being 10—10* rads; and for bone and bone marrow, a few rads to about 60 rads. If we assume a nonuniformity factor of five for bone, the dose estimation could be five times higher. I am pleased to see that the thyroid doses you estimated in your report correspond moreorless to our estimates in order of magnitude. However, I assume there would be some uncertainty in this type of dose estimation. What level of accuracy do you assign to your dose estimation? Did you also observe