In the present experiment the author pursued changes occurring in the functions of pseudo-eosinophils of the bone marrow of the rabbits infected with various pyogenic bacteria and obtained the following results: 1. In the periodical observations on the functions of pseudo-eosinophils of the bone marrow after intravenous injection of Streptococcus viridans (0.5 mg/kg) for consecutive days of one, four, seven, and fourteen respectively, the wandering velocity is slightly increased in the entire course. On the other hand, the carbone particle phagocytotic ability falls to the lowest level after the fourth and seventh injections and it tends to recover after the fourteenth injection; and in the neutral-red vital staining pseudo-eosinophils stain quickly and deeply, proving likewise the fall in function and the change takes place in parallel with the change of phagocytotic ability, and this fall in the functions from the standpoints of carbon-particle phagositosis and vital staining occurs when the systemic conditions and anemia in the test animals are aggravating and it also coincides with the stage where the production of leucocytes in the bone marrow is vigorously carried out. 2. When the results of four consecutive daily injections of the heat-killed Streptococcus viridans (0.5mg/kg) are compared with those of four similar injections of living bacteria, these changes as mentioned above are slight. Four consecutive injections of Streptococcus haemolyticus (0.5mg/kg), Staphylococcus aureus (0.5mg/kg), or Staphylococcus albus (1.0mg/kg) give the similar findings as in the case of four consecutive injections of living Streptococcus viridans; and there are no marked differences by strains of bacteria. From these it may be inferred that the dissociation in the functions of leucocytes is due to the overproduction of leucocytes, because the cells are being rapidly multiplied but immature from functional point of view.