Clostridium perfringens is an important member of the group of organisms called by the generic name Clostridium. They are sporing organisms which will grow only in the absence of oxygen; some species are more exacting in their requirements for reduced oxygen than others. Under the microscope the morphological appearance varies from the typical large rod-shaped bacilli with rounded or square ends (C. perfringens) to irregular forms including boat- and lemon-shaped organisms, swollen rods, and filaments. Mostly they are arranged singly, but some occur in pairs or in chains and bundles.