Mary Ann Murphy, age 14, of Santa Rosa, Calif., for her question:

WHAT CAUSES GANGRENE?

Gangrene is the death of the tissues in a part of the body, such as a toe or foot. Some of the causes of grangrene are diabetes, plugged arteries in old age, freezing and frostbite, bad wounds and infections.

Death of tissues in a part of the body is called mortification.

In dry gangrene, the part turns black and loses all feeling. The healthy tissue near the gangrene shows a red inflamed zone, called the zone of demarcation.

With medical attention, the dead tissue will slough off of the body. Theoretically, if the diseased part came off by itself, it would separate from the rest of the body just beyond the zone of demarcation.

Moist gangrene has the same symptoms as the dry kind, but in addition, there may be blisters, oozing fluid and disagreeable odors. Bacteria which cause the flesh to decay play an important part in moist gangrene, but not in dry.