Several methods for tissue culture of bone marrow were comparatively examined in order to study the mechanisms of phagocytosis of carbon particles in detail. From the results obtained here, a consideration was made on the mechanisms of phagocytosis as follow : 1) Culture method with coverslips hitherto described, when applied with the Indian ink mixed with the culture medium as well as with the ink added after the coagulation of plasma, proved insufficient for the observation with oil immersion system and for the quantitative investigation. 2) A modified procedure with Unno's slide-glass proved more successful in that quantitative study could easily be made and more datailed observation of phagocytosis with phase contrast microscope could be accomplished. 3) Phagocytosis of carbon micro particles from the culture medium by the neutrophilic leukocytes was observed very clearly, but in case of monocytes it is quite different in that the submicroscopic microgranules of carbon were chiefly adsorbed on the surface of their secretion granules. In addition, in the vacuoles of neutrophilic leukocytes Brownian movement of carbon particles was observed. This was not so in case of monocytes. 4) The continuous observation of the process of phagocytosis described here afforded a better understanding on the mechanism of phagocytosis which would not be obtained by the usual methods hitherto described such as supravital observation or the fragmental observations after the intravenous administration of Indian ink.