The Effects of Single and Divided Doses of X-Radiation on Bone Marrow of Partially Shielded Rats

A total of 48 rats was exposed in a variety of ways to 200-kwp x rays. Bone marrow in an exposed lower quadrant which received 900 r in five daily fractions of 180 r while the remaining three-fourths of the rat was shielded showed less recovery at 10 to 12 days than marrow which received 525 r of total- body irradiation in a single dose. The fact that partial shielding and dividing the dose did not give more protection suggests that these two protective mechanisms are not additive. Mild irradiation appeared to produce slight but measurable resistance to a heavy dose of x ray at 3 days or 10 days after the mild treatment. Plasma cells were cantly in the marrow 5 and 10 days after irradiation by transformations fromn hemocytoblasts, and possibly from early emythroblasts and myelocytes. (auth)