By adding the serum of patients with varicus blocd diseases to the medium of bone-marrow tissue culture of rabbits, the author studied mainly its influence on the vital staining of pseudoeosinophils with neutral red. At the same time the author pursued vital staining of neutrophils in the bone marrow of the sternum from the same patients with neutral red; and as for the verification of the study, the cells that had been cultured for several hours were vitally stained. As the result the author arrived at the following conclusions: 1. When the cell functions (wandering velocity and carbon-particle phagocytosis) are low during the tissue culture, vital staining by neutral red takes place fast and highly but the stained color fades quickly. 2. Also when the vital staining is done after fixed intervals of culture, the longer the time of culture is, namely, at the time when the cell functions are further diminished, the more prompt and the higher is the staining and also the fading takes place more quickly. 3. Those patients showing lowered cell functions on the vital staining of bone marrow are aplastic anemia, Banti's disease, leukemia, acute bleeding anemia and kala-azar. 4. Likewise those who show a slight lowering in the cell functions are ancylostomiasis, essential hypochromic anemia and Werlhof's disease; and those whose functions are hardly lowered are those patients suffering from lung tuberculosis and malignant nephrosclerosis, namely, not from blood diseasses. 5. On vital staining the sera that possess factors of lowering the functions of bone marrow are those of aplastic anemia, Banti's disease, acute bleeding anemia, Werlhof's disease, and leukemia.