individuals and in some instances another agent had been incriminated as leukemogenic; that it was believed that a series of small doses of radiation might give cumulative effects appreciably larger than could be produced by one of them alone; that the cumulative effect on an individual who was extensively exposed to radiation for about three years would depend on the magnitude of the exposure, the extent of the body that was exposed, and other factors, and that no specific prediction could be made for a particular individual in such an instance but that the probability of developing certain sequelae of radiation exposure, such as induction of leukemia, would increase significantly; that it would be difficult to state either a minimum or a maximum interval between exposure and development of leukemia where the exposures were small and multiple; and that where leukemia developed in an individual who had had small and multiple radiation exposures it would be very unlikely that it would be attributable to radiation if the onset were immediately after exposure and that it was likely that in such a case the latent period would be longer than in leukemia due to single dose radiation exposure. At the request of the BVA, the Armed Forces Institute of Pathology reviewed veteran’s medical record and thé autopsy, and expressed the following opinion: The members of the staff have substantiated the diagnosis of acute monocytic leukemia (myelomonocytic type) from the examination of the available material. No evidence of radiation injury, however, was observed. The members of the staff are unable to determine the cause of the leukemia process in this man and to the best of our knowledge the inconclusive in view of the unavailability of complete dosimetry records. In addition, the effect of small and multiple radiation exposures has not been scientifically established. The absence of evidence of radiation injury on postmortem examination is also inconclusive inasmuch as residual tissue damage studies have not been verified to the extent that dogmatic statements may be made regarding them. There remains for discussion a consideration of the aberrant blood studies, the only evidence of abnormality relevant to the question at issue. It is generally accepted that in the adult the normal white blood cell count ranges from 5,000 to 10,000 and that of these cells 60 percent are neutrophils, 30 per cent are lymphocytes and the remaining 10 per cent are monocytes, (usually from 1 to 4 per cent), basophils and eosinophils. In this case, all "hs matologic examinations between December 1950 and terminal hospitalization. disclosed a lymphocyte count in excess of that generally accepted as normal, with values as high as 50 per cent in 1951 and 51 per cent in 1952. The significance of this tendency toward lymphocytic increase as early as 1951 is enhanced by information contained in radiation hazard studies that there is some evidence which indicates that a diseased or poorly functioning organ may be more susceptible to radiation injury than a normal one. In view of the limitations of present scientific knowledge of the effects of ionizing radiation induced leukemia, the Board is impelled to conclude that the evidence of record is insufficient to either prove or disprove a causal relationship between the ionizing radiation exposure during service and the fatal leukemia but that it is within the range of probability that in this case there was such a relationship. etiology of leukemia is unknown. Findings of the BVA and Basis for Decision: \n finding that with resolution of reasonable doubt, the fatal leukemia was due, at least in part, to exposure to ionizing radiation during service, the Board observed: The cause of the veteran’s death in May 1963 was acute monocytic leukemia (myelomonocytic type). Symptoms of this disease did not become manifest until many years after March 1954, when he retired from service after 30 years of active duty. Thus, favorable resolution of the question at issue is contingent on a finding that there was a causal connection between the fatal disease and exposure to ionizing radiation, an established leukemogenic agent under certain circumstances, during active service. Such exposure was possible only between November 1950 and November 1953, during which time the veteran was a participant in experiments involving the use of atomic material. There is a record of the amount of radiation he received in 1951 but there is no available record of the amount of additional radiation which might have been received during his assignment to research and development orojects in 1952 and 1953. The total exposure to ionizing radiation shown by the record now available indicates that the veteran’s exposure was below the level generally accepted as injurious to critical organs. This evidenceis 76 77