Bite injury. Swollen, infected hand due to a human bite to the left index finger. Bacteria have multiplied in the wound causing pus (white) to form. Pus is a mixture of white blood cells that fight infection, the bacteria causing the infection, and tissue debris. The end of the index finger has turned gangrenous because its blood supply has been disrupted resulting in tissue death (necrosis). The infection may be cured by antibiotics, but gangrene is usually treated by surgical amputation of the affected digit or limb.