The mechanism of phagocytosis, that is, the engulfing of bacteria, cells, tissue products, etc., by leukocytes, is usually interpreted in terms of chemotaxis. Substances present in the environment are believed to exercise a sort of directive influence, either attractive or repellant, on the phagocytic cells. Since the stimuli most likely to reach the leukocytes from a foreign agent and bring about an alteration in their movement and performance are chemical in nature, the importance of "chemotaxis" in phagocytosis and leukocytosis is everywhere emphasized.
This familiar attempt at an explanation of the behavior of leukocytes cannot readily be applied to the undeniable phagocytosis of insoluble, chemically inert particles like coal dust or carmin granules. Leukocytes have frequently been seen to enclose these with the same avidity that they engulf bacteria. It has been surmised, without further evidence, that the foreign particles in some way acquire a coating from some component of