the absorption, distribution, retention, and excretion of these radioactive materials. In addition to evaluating the metabolic characteristics of these substances, it was necessary to duplicate as nearly as possible, with laboratory animals, the manner by which fission product poisoning might occur. This included a study of the behavior of these radioel ements following their introduction into the body by the three major portals of entry, namely inhalation, oral ingestion, and tae ee ee 2krans nm Rh AN Hae Naren, at es a eeapeepmere eedee termiete ts it themerina om oe Ce ge Arm gy ae ee . ~ ara neato through cuts and abrasions of the intact skin ..-e, No satisfactory estimates or predictions of the possible metabolic characteristics of most of the fission products could be made, since most of these substances are radioactive isotopes of elements concerning whose metabolic properties very little was known. In other words, there were no reliable data avaflable that could’ make it possible tn most instances to predict which of the fission products would be absorbed from the digestive tract and rapidly eliminated, once having gatned entry into the body, and which ones might be selectively deposited and retained in some vital structure. Actually, there was only one fission product, radioiodine, that had received sufficient study with regard to its metabolic properties, prior to 1942, to permit a reasonale evaluation of the amount that could be tolerated within the body without producing damage. A second fission product, radiostrontium, had been studied before 1942, but not in sufficient detafl to satisfy the requirements of the medica) Plutonium Project. research progran of the The nature of the metabolic characteristics of the other fission products at that date was essentially a completely unknown quality .... In addition to the fission products, it was necessary to evaluate by similar tracer studies the potential dangers from plutonium poisoning. This element fs radinactive and