How can people die from gangrene?

Gangrene is often called 'gas gangrene' because it puts out a foul gas when an area is infected. Gangrene is an anaerobic bacterium, which means it grows in places hidden or away from air, let's say like deep down in a wound on your leg. If the infection is allowed to start growing, because circulation was cut off to the wound or wasn't cleaned properly, or treated with antibiotics to kill it, the tissue starts to die, cutting off the air to more tissue (which the bacteria likes) and putting toxins (poisons) out into the body systems. Once gangrene has set it and the leg has turned black, these poisons have to be removed by cutting off the leg, so that the infection won't poison the entire body and kill it.