Some Data on Mechanism of Leukopenia and Leukocytosis following Irradiation.

T HE LEUKOPENIA developing some days after a high dosage of ionizing irradiation is apparently due to direct injury of the bone marrow. On tile other hand, the appearance of leukocytosis before leukopenia develops mdicates that other factors may influence the level of circulating leukocytes in that phase. Tile short course of this initial leukocytosis suggests the possibility of an increased peripheral removal as shown by Cronkite et al.1 No direct effect of ionizing radiation on the granubocytes, in the commonly used dose range, has been shown thus far. The increase in granulocytes which appears within the first 24 hours following irradiation has generally been explained by