Abstract
Three-dimensional scale models of bone marrow from a hypertransfused and a normal rat were constructed. The model of marrow from the hypertransfused rat demonstrated the existence of distinct erythroblastic islands in situ in which the erythroblasts underwent sychronous maturation. Macrophages were found in close association with the developing erythroblasts. The immature erythroblasts were tightly grouped, but as they matured they began to move apart. Erythroblasts in individual clusters were found to be at the same stage of morphologic maturation. In contrast, the model of marrow from the normal rat showed a majority of clusters containing erythroblasts at various stages of maturation. Erythropoiesis was not spatially restricted to the area proximal to the sinuses but was found to occur over the entire marrow space. Thrombopoiesis, however, was found to take place exclusively in the immediate vicinity of the marrow sinuses.
