Quantitative Studies on the Radiation Pathology of the Bone Marrow of Small Laboratory Animals: II. Marrow Response to Whole-Body X-Irradiation in Rodents of Different LD 50

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Abstract
The acute bone marrow response to X-rays (LD50 dose) was investigated by film ratio and electronic counting in strains of mice of different radiosensitivity (BALB/c, A/Crgl/2, C57BL, BCF1) and in the Chinese hamster (Cricetulus griseus), which has the highest LD50 so far known in mammals. The pattern of change seen in the nucleated cell count is consistent with the assumption that similar physiological mechanisms were at work in each irradiated strain but that genetic factors introduced quantitative differences in response. The Chinese hamster had the lowest control nucleated count and a recovery rate of this count that was no better than that of the mice. When the undifferentiated stem cell count (as revealed by the film-ratio method) was examined, however, it appeared that the hamster''s recovery was remarkable; a marked hyperplasia of these stem cells was observed on days 4, 6, and 8 after exposure. Some recovery was seen 12 hours after exposure. It is suggested that this peculiar response is related to the high radioresistance of the species.