Gas gangrene in amputated arm of injured soldier
In WWI, most cases of gas gangrene were caused by infection with Clostridium perfringens, and Group A streptococcus. Other bacterial infections were occasionally found, as well.
The infecting bacteria could be pretty easily differentiated by the type of pus that was exuded or found when the necrotic tissue was cut into. C. perfringens produced very thin, "dishwater"-like pus, and smelled "sweetly putrid". The other bacterias produced much thicker pus, and did not smell sweet.
Not that it made any difference what bacteria was causing the gas gangrene - in the Great War, antibiotics weren't nearly effective enough to halt the progress of infection, and amputation was the default treatment modality for cases brought in from the front.
British Medicine in the War, 1914-1917. British Medical Association, 1917.