In the bone marrow tissue culture of various leukemias as well as of several blood diseases conducted with the purpose to see the degenerative changes of the leucocytes appearing in the growth area, the following results were obtained. 1. In the case of acute myelogenous leukemia the degenerative changes of myeloblasts proceed rapidly at an early stage of culture and there appear degeneration granules which can never be observed in normal myeloblasts. Vacuoles and abnormal processes do appear though small in number. 2. In the case of acute lymphocytic leukemia, the appearance of small degeneration granules is marked in the degenerative changes of lymphoblasts. The degenerative changes of lymphocytes proceed slightly slower than in the case of the blasts, and the nonhomogenous condensation or swelling of the nuclei can often be seen. 3. In monocytic leukemia, degenerative changes of monoblasts appear earlier than those of monocytes, and degeneration granules, small vacuoles and various abnormal processes appear most numerously as compared with other kinds of blasts. The changes of promynocytes are relatively rapid and also degeneration granules, small and intermediate vacuoles as well as various abnormal processes can be recognized. In the case of monocytes the changes occur relatively earlier than in the case of those in normal person, and appearance of numerous degeneration granules is typical, large and small vacuoles can also be observed. 4. In the case of chronic myelogenous leukemia, the degenerative changes of myeloblasts take place slower than in the case of acute myelogenous leukemia, but more rapidly than in normal person, In promyelocytes and myelocytes the changes proceed relatively slowly, and in metamyelocytes and neutrophils, the changes proceed somewhat rapidly. Generally, in the case of immature cells degeneration granules, vacuoles and abnormal processes are less in number, but in more mature cells the number of them increases. In the case of mature neutrophils spherical processes appear markedly many and eruption of nucleus is seen rather few. 5. In chronic lymphocytic leukemia degenerative changes of lymphocytes appear somewhat more rapidly than in the case of normal person but they appear slower than those in acute cases, and most of lymphocytes show homogeneous pyknosis. 6. In aplastic anemia the degenerative changes of neutrophils proceed rapidly, having large degeneration granules as well as many vacuoles. Vacolization can also be observed in a high degree. Many abnormal processes appear and the nuclei are also either swollen or erupted. 7. In essential hypochromic anemia the degenerative changes of neutrophils appear rather rapidly and degeneration grenules, small vacuoles, and spherical processes are relatively numerous. 8. The degenerative changes of neutrophils in Banti's disease progress rather rapidly and the disorder in the arrangement of specific granules can be recognized at an early stage. Degeneration granules appear rather rapidly and the nuclei are swollen relatively earlier. 9. idiopathic thrombocytopenic purpura the degenerative changes in neutrophils take place approximately in the same manner as in the case of normal person.