Effect of minimal irradiation on differentiated cell levels. To determine the hematologic effects of low doses of irradiation on the normal host, animals in groups of five received low doses of whole animal irradiation (0, 20, 50, and 100 cGy) without donor cells. At days 2, 7, and 14, animals were killed and tissues were analyzed for white blood cell count (×10³/μL), platelet count (×10⁹/L), and marrow cellularity (×10³; 2 tibias and 1 femur).