| Abstract: | Various numbers of cells of intact or irradiated bone marrow from syngeneic donors were injected into mice irradiated with a lethal dose. A linear relationship was found between the number of 8–9 day colonies growing in the femoral marrow and the number of injected cells, and an exponential relationship was found with the dose of irradiation. The pattern of cloning of the stem cells in the bone marrow was similar to that in the spleen. Differences were found in the radiosensitivity of colony-forming units (CFU) depending on the organ (spleen, bone marrow) in which they formed the colonies. CFUs settling in the bone marrow were more resistant (D0 160–200 R) than CFUs settling in the spleen (D0 80–100 R). Differences in the radiosensitivity of the CFUs are due, it is postulated, to the presence of a heterogeneous population of stem cells and also to specific features of the organ (spleen, bone marrow) in which the colonies are formed. |
