A geometric model that takes into account the changes in size, shape and position of the uterus during pregnancy has been designed for calculating the radiation dose to the uterus and the fetus from a radionuclide in the mother's bladder. The bladder is assumed to fill at a constant rate to 300 ml before voiding. The average dose in rads per photon emitted from a source in the bladder during one bladder filling has been calculated for monoenergetic photons of 0.02, 0.03, 0.05, 0.1, 0.2, 0.5, 1 .O, 1.5, 2.0 and 4.0 MeV. Since the dose to specific organs of the fetus could not be calculated, the fetal space was divided into 12 compartments. The dose was calculated for each compartment, for the average of the entire fetal space, and for the uterus. The average dose per photon to each compartment decreases as the fetus increases in size. The highest dose rate to the uterine wall occurs at the point where it touches the bladder. Because the uterus enlarges, the point on the uterus receiving the highest dose rate changes during pregnancy.

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The fate of alpha-emitting radioisotopes in the human body continues to be a problem of great interest to atomic industry.' Most guide lines for permissible human body burdens for alpha emitters are based on human experience with radium2 and thorium, and extrapolation from animal experiments with rare earths. The 45 years of experience with these elements in man has shown us that most acute or late effects produced by these radioactive elements in animals ultimately occur also in man, but usually after longer induction periods. The actual fate and toxicology of specific transuranic elements in man remains poorly defined, chiefly because excellent industrial health practices have limited the opportunity for human histopathologic studies of either acute or chronic effects of these elements. The cases presented here are unusual only in this regard. They represent a group of eight cases (TABLE 1 ) of accidental intradermal contamination with minute amounts of metallic plutonium-239. In some of them the wound made at the time of contamination was immediately debrided surgically but was subsequently found by careful radiation monitoring to still harbor minute metallic remnants. In others, attention was drawn to the site of the previously debrided wound by development of a millimeter-sized intradermal, sometimes painful, nodule that became progressively more superficial and prominent.Some of the injured men were highly skilled machinists inured to the hazard of being struck by sparks from metals containing iron being turned on lathes. They were trained to avoid such happenings with these heavier metals, and were aided by protective clothing, remote controls, and other safety procedures. Although some of the contaminations occurred in glove box accidents, where contamination was obvious, some embedded particles were detected only in retrospect by careful routine surveillance. Where found, the depth of the penetration was appraised and the area was excised surgically and submitted routinely to radioassay and histopathology.External monitoring of an area suspected of having embedded plutonium was done with a thin NaI crystal detector system operated to measure the lowenergy x-rays of plutonium.3~~ The plutonium content of the most recent biopsy specimens was also estimated by means of the 60-keV gamma ray of the plutonium contaminant, americum-241.5 In both methods the estimated amount of plutonium in the tissue was based on comparison with known standards. After analysis the tissue, fixed at time of surgery in 10% formalin, was submitted to autoradiography with both stripping film and liquid techniques using fine grain * An operating unit of Oak Ridge Associated Universities, Inc., Oak Ridge, Tenn., under contract with the United States Atomic Energy Commission. 791