_Cold._ Frost bite causes gangrene of varying degrees. A small circumscribed patch of tissue may succumb, or an entire finger or extremity may be affected. The variety is invariably moist. The diagnosis is easily made from the history of exposure (See “Frost bite”). _Chemicals._ Carbolic acid, even in weak solution, often causes gangrene of a finger or toe, because of its frequent use as a wet dressing, and therefore should never be employed in this manner. Gangrene of a single part, (especially in a young subject), incident to a slight injury or infection, should always excite suspicion that phenol has been employed. Moist gangrene is the rule. The part presents a hard, shriveled, black appearance which is characteristic. Weak solutions of other chemicals such as lysol, acetic acid, and potassium or sodium hydroxide, employed as a wet dressing, are also capable of producing gangrene. +Symptoms.+ (_Dry Gangrene_). Typical dry gangrene usually develops in the toes and the feet, and the principal symptoms which point to its advent are, coldness, numbness, pain and tingling in the feet and muscles of the legs. Persons about to be affected with dry gangrene often complain for months, before any local signs of gangrene are present, of severe burning pain in the feet at night when warm in bed. A trivial injury, such as a bruise, the friction of the shoe, or the cutting of a corn, may act as the exciting cause of the affection. The part becomes congested and gradually assumes a dark purple color, finally becoming black and dry; it is insensitive, but the surrounding parts are congested and may be the seat of intense pain. The dead part becomes black, shriveled, and dry, and emits little odor. Dry gangrene usually spreads very slowly; one or two toes may first be involved and the disease may gradually spread to the rest of the foot and the leg. There may be little fever at first, but if a large extent of tissue is involved, a certain amount of fever develops. During the progress of the disease, pain is usually present to a greater or lesser degree, sometimes being intense; this is accounted for by the fact that the nerves are usually the last structures to die. During the course of the disease, the patient loses much sleep from continued pain, and becomes worn out and may die of exhaustion. In dry gangrene there is usually no well marked attempt at the formation of lines of demarcation and separation, but in some cases, if the amount of tissue involved is small, say one or two toes, or a part of the foot, for instance, and if the patient’s strength can be sustained, the line of separation forms, and the dead tissue may be cast off, leaving the bones exposed in the wound.