THE MOBILIZATION AND TURNOVER TIMES OF CELL POPULATIONS IN BLOOD AND BLOOD-FORMING TISSUE

1. A description is given of a technique for performing absolute and differential counts of the nucleated cells of guinea-pig bone marrow. Emphasis is placed on the importance of using animals of uniform age in marrow studies. 2. In a 400 gm. male guinea-pig of the Dunklin-Hartley strain, the total marrow volume is 7.0 cc., the total blood volume 28.8 cc., and exchanges of cell population between marrow and blood can be readily calculated on the basis of these figures. 3. Thoracic duct lymphocyte production per day is about 4 times the total lymphocytes normally present in the blood and about one sixth to one eighth of the total marrow lymphocyte population. 4. Lymphocytes in bone marrow are practically all small, and are not formed in the marrow, but come to it from the blood stream. 5. In respect to granulocytes, the marrow possesses about 150 times the number normally present in the blood, and two thirds of this myeloid reserve consists of mature or almost mature cells which can be rapidly discharged into the blood stream. 6. Leucocytosis Promoting Factor (Menkin) evokes in 4 hours a dual response by the marrow, namely a discharge of granulocytes into the blood and an uptake of lymphocytes from the blood. But most of the granulocytes thus entering the blood rapidly leave it. 7. Unlike the granulocytes, there is no large erythroid reserve in the bone marrow, and the quantitative data indicate that under normal conditions erythrocyte production just about keeps pace with requirements. 8. In animals subjected to hypoxia at the Jungfraujoch, about 3 days elapse before there is an appreciable discharge of additional erythrocytes into the blood. The nucleated erythroid cells of the marrow begin to increase on the second day, and reach a peak on the fourth day. 9. Morphological evidence indicates the existence of "Transitional" lymphocytes, intermediate between the small lymphocyte and the blast cell.