By performing tissue culture of the bone-marrow aspirated from the sternum of normal persons, ribs removed at the thoracoplastic surgery, and from the femur of normal rabbit, the author observed the course of the bone-marrow tissue culture, and obtained the following results. 1. In the bone-marrow tissue culture of the human sternum the growth area keeps on increasing up to 18 hours of the culture and its average relative growth rate is 10.64; in the case of the rib removed at thoracoplastic surgery it lasts for 36 hours and the average of its relative growth rate is 16.90; and in the case of the rabbit femur it lasts for 48 hours and the average of its relative growth rate is 45.37. The fluctuation curve of the average relative growth rate in each case is somewhat like a parabola. 2. The average of the cell density index in the case of human sternum is 52 at 18 hours after the start of calture; in the case of the rib removed at the thoracoplastic surgery it is 54 after the 24-hour culture; and in the case of the rabbit femur it is 67 after the 24-hour culture. 3. In the case of the sternum of normal persons the average value of wandering velocity of neutrophils reaches the maximum of 15.24μ/m three hours after the start of the culture and neutrophils cease wandering on the fourth-sixth day of the culture; in the case of the rib removed at the thoracoplastic surgery the average of the wandering velocity reaches the maximum of 10.51μ/m, and the wandering of neutrophils ceases in the sixth to seventh day of the culture; and in the case of normal rabbit femur the average wandering velocity of pseudoeosinophils reaches the maximum of 14.17μ/m immediately after the start of the culture and the wandering of pseudoeosinophils stops on the 5th to 6th day of the culture. 4. The cell growth area is divided into the central, intermediate and peripheral zones. The course of cell activity in the growth area is divided into the initial, middle, and terminal stages, and obsewations have been carried on from stage to stage.