Phagocytosis. Coloured scanning electron micrograph of a polymorphonuclear white blood cell or leucocyte, attacking Bacillus cereus bacteria. The leucocyte (orange), part of the body's immune system, is attaching to and engulfing the Bacillus cells (blue, rod- shaped). It uses enzymes to digest the bacteria. This process of engulfment and digestion is known as phagocytosis. Highly mobile, phagocytic cells migrate to areas of tissue damage.