For the purpose to get the information about the control mechanism of erythropoiesis in bone marrow the author introduced a mass of homologous red cells into anemic animal and observed how the bone marrow cells and circulating blood react against the prompt normalization of the anemic condition. After the red cell transfusion which was enough to restore the anemia promptly the red cell number in the circulating blood continued to increase until 72 hours after the transfusion, reaching an extremely high level in both red cell number and hemoglobin contents. Mitotic index and the DNA synthesis as
observed by tritiated thymidine incorporation into DNA proved no actual change even 24 hours after the red cell transfusion, though a marked decrease in labeling
index was found in large size precursors. Histologic picture revealed the proliferation of reticulum cells. 48 to 72 hours after the red cell transfusion both mitotic index and DNA synthesis of erythroblasts have largely retarded in all series of specialization with the decreased appearance of the erythroblasts in bone
marrow sections. The measurements of red cell size and the RNA contents of erythroblasts and reticulocytes proved the accelerated denucleation at the early stage of erythroid cell specialization, as early as basophilic stage resulting in a marked macrocytosis.</p
