Stem cell in peripheral blood: a study by parabiosis of irradiated and non-irradiated animals. II. Hematopoiesis of irradiated rat having a non-irradiated parabiont

For the purpose to confirm the existence of the stem cells of the myeloid and erythroid cells in the circulating blood and to have the information of its morphologic entity, the author conducted morphologic observations on the peripheral and bone marrow cells of the x-irradiated parabionts having non-irradiated partners joined by the vascular parabiosis devised by the author, and the following results were obtained. 1. The control rats exposed to 1000R x-ray did not show any sign of recovery of hemopoiesis in bone marrow even 8 days after irradiation. 2. In the bone marrow and spleen of the lethally irradiated animals having non-irradiated partner in parabionts, precursor cells of granulocyte and erythrocyte appeared first 4 days after conjugation irrespective of the days after irradiation, and the hemopoiesis was restored completely on the sixth to the seventh day. The results have indicated that the circulat. ing blood has the stem cells which can dedifferentiate and transform into the precursor cells of the myeloid and erythroid cells within 3 days under adequate conditions. 3. On the basis of the morphologic observations on the peripheral blood of the parabiosis and non-irradiated rats revealded non-specific cells, a discussion was made on the possibility that some atypical lymphoid cells can serve as the stem cells of the myeloid and erythroid cells.