1. Phagocytosis is carried out in the following process: the cell membrane of the pseudopod contacts and adheres to a foreign body ; it encloses the foreign body with its fused tips; its fused tip portion is separated from the cell membrane of the pseudopod and transferred into the cytoplasm. 2. Development of the pseudopod is the prerequisite in phagocytosis. The pseudopod which show a favourable phagocytosis is the one whose cell membrane has a low surface tension and easy adhesiveness to a foreign body. When the cell is possessed with such pseudopod, pinocytosis is very likely to occur which enables the cell to engulf a foreign body including its medium without touching it. 3. The adhesiveness of a foregin body constitutes another important factor. Especially when a foreign body is of a big size its low adhesiveness has only a few chances of developing surface phagocytosis. 4. Phagocytosis is carried out only through the pseudopod of a cell. The pseudopod is what is pushed out of the easily liquidifying substance in the cytoplasm by contraction of an actomyosine like contractile protein which is considered to exist in the surface layer of the granuloplasm. The energy of this contraction is ATP which is also needed for the maintenance of surface tension and adhesiveness of the cell membrane. A decrease in the production of ATP results in a decrease in the activities, surface tension and adhesiveness of the cell membrane of the pseudopod. It is concluded that phagocytosis is performed by a mechano-chemical system which is coupled by ATP. 5. A decrease in energy is not always proportionally accompanied by a decrease in phagocytosis. Occasionally an adverse relationship is observed, since phagocytosis is subjected to various interacting factors, such as the size, number, developmental speed and frequency, surface tension and adhesiveness of the pseudopod, and the nature of foreign bodies to be devoured. 6. Discussions are made of the findings of cells, phagocytic vacuoles and devoured bacteria following phagocytosis with a phase contrast microscope and an electron microscope.