Previously in our laboratory Tachibana has proven that the bone marrow like other blood-storage organs discharges a great quantity of blood in acute bleeding and that it also occupies an important position among the blood-storage organs. In order to endorse Tachibana's results still further the author has investigated the changes in the erythrocyte counts, hematocrit values, average diameter of erythrocytes, Price-Jones curve, average volume of erythrocytes. and volume index in the nutrient veins of the femur as well as the findings on the bone marrow of adult rabbits after a rapid depletion of blood in the same manner as Tachibana, and the results of the observations are as follows: 1) When a rapid depletion of blood to the amount of 15-20 c. c. /K. is performed in rabbits, an increase of erythrocyte count as well as increase in the hematocrit value can be observed in the nutrient venous blood of the femur, and these increases are especially marked 1-2 hours after depletion. However, through entire course no striking change can be recognized in the Price-Jones curves, averages of the diameter, the volume, and the volume index of erythrocytes; and from these data the increases in erythrocytes and in the hematocrit value are thought to be due to the mobilization of the blood stored in the bone marrow venous sinuses. 2) In the findings of the bone marrow tissues in the rabbit rapidly depleted of blood the decrease of blood in venous sinus is most marked or totally disappeared 1-3 hours after depletion while it later recovers gradually until finally it presents a blood repletion picture somewhat similar to that of the normal. In other words, the blood in the veins of the bone marrow is rapidly mobilized to the outside of the marrow after depletion, and later new blood corpuscles from the hematopoietic foci are recognized to be transferred and stored in the venous sinuses. 3) These results clearly support the experimental results of Tachibana of our labor atory: and therefore, it is thought that the bone marrow, being a blood-storage organ, has an important significance in the repletion of blood in general circulation.