Bacterer-i~ of enteric origin has been found to occur in a high percentage of mice during the 2nd week following a single exposure to a moderate dose of ionizing radiation (1). This was demonstrated on 288 mice, of which 20 were killed for heart's blood culture each day following 600 r x-irradiation, and on 595 mice, of which 35 were killed and cultured each day after 450 r. The percentage of positive blood cultures was higher among the mice receiving the larger dose of x-ray, but in both series its maximum was reached during the period of greatest mortality. These results, however, merely indicated the presence or absence of bacteria in the circulating blood at the time of sacrifice. The next step toward an understanding of the pathogenesis of these spontaneous bacteremias was the determination of their time of onset and duration. Irradiated mice were accordingly subjected to a series of daily blood cultures.
Materials and MetkodsMice.--lO week-old female Rockland "RAP" mice, weighing 20 to 25 gin. were used.They were segregated after irradiation and kept in individual jars to exclude direct contact as a source of cross-infection. Their bedding, which was changed once a week, was wood shavings which were sterilized by autoclaving and dried before use. They were fed on Rockland mouse pellets. Water was provided in sterilized water bottles and tubes which were changed daily. The mice were cultured in groups of convenient numbers (8 to 16).Irradiation.mEach of 7 groups of mice irradiated on different dates was exposed to a single dose of total body irradiation, carried out in the X-ray Division of the Argonne National Laboratory.* They received 550 r delivered at 250 kv., 15 ma., at a distance of 27 inches, using ram. copper and 3 ram. bakelite filters, at a rate of approximately 20 r per minute. During irradiation they were confined in perforated plastic tubes on a circular plate which rotated slowly within the irradiated field.
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