The phagocytic behaviors of the neutrophilic leukocytes in the tissue cultures of sternal marrows of patients, especially of those suffering from blood diseases were investigated. Moreover, additional investigtion was made on the sera of these patients in regards to their influences upon the phagocytosis of pseudo-eosinophilic leukocyte in the tissue culture of rabbit bone marrow. The results are summarized as follow: 1) Such diseases with characteristic leukopenia were examined in the first place. Hypoplastic anemia caused a remarkable decrease in the phagocytic activity of neutrophilic leukocyte. The serum obtained from the patient of this disease, when added to the tissue culture of rabbit bone marrow, also reduced the phagocytic activity of pseudo-eosinophilic leukocyte. In case of Banti's Syndrome a considerable loss of the phagocytic activity of neutrophilic leukocyte resulted and no appreciable influences of the serum on that of pseudo-eosinophilic leukocyte of rabbit bone marrow were observed. Kala-azar and agranulocytosis induced a suppression of the phagocytic behavior of neutrophilic leukocyte, respectively. 2) In the second test dealing with leukemia, the neutrophilic leukocytes, both the myeloic as well as the monocytic ones, of bone marrow suffered from some decreases, a slight decrease in the chronic form of this disease and a heavy one in the acute form, in their phagocytic activities. Addition of the serum also caused a lowering in the phagocytic activity of pseudo-eosinophilic leukocyte of rabbit bone marrow. 3) In the third place several diseases accompanying no remarkable changes in leukocyte number were tested. Essential hypochromic anemia was found to suppress the phagocytic behavior of neutrophilic leukocyte of bone marrow. The serum also proved unfavorable for phagocytosis of pseudo-eosinophilic leukocyte. Lowering of phagocytic activity fo neutrophilic leukoeyte was seen also in hook-worm anemia and post-hemorrhagic anemia in a parallel manner to the conditions of anemia. In these two diseases the sera had no effects on the phagocytic behavior of the pseudo-eosinophilic leukocyte of rabbit bone marrow. Idiopathic thrombocytopenic purpura proved to have no appreciable effects on the phagocytic activity of neutrophilic
leukocyte and this was also the case with regard to the addition of the serum. 4) Other diseases than the blood diseases seemed to have little to do with the activities of phagocytic behaviors of the leukocytes.