Clinical Features.—­The commonest seat of the disease is in the toes, especially the great toe, whence it spreads up the foot to the heel, or even to the leg (Fig. 20).  There is often a history of some slight injury preceding its onset.  The vitality of the tissues is so low that the balance between life and death may be turned by the most trivial injury, such as a cut while paring a toe-nail or a corn, a blister caused by an ill-fitting shoe or the contact of a hot-bottle.  In some cases the actual gangrene is determined by thrombosis of the popliteal or tibial arteries, which are already narrowed by obliterating endarteritis.

It is common to find that the patient has been troubled for a long time before the onset of definite signs of gangrene, with cold feet, with tingling and loss of feeling, or a peculiar sensation as if walking on cotton wool.

The first evidence of the death of the part varies in different cases.  Sometimes a dark-blue spot appears on the medial side of the great toe and gradually increases in size; or a blister containing blood-stained fluid may form.  Streaks or patches of dark-blue mottling appear higher up on the foot or leg.  In other cases a small sore surrounded by a congested areola forms in relation to the nail and refuses to heal.  Such sores on the toes of old persons are always to be looked upon with suspicion and treated with the greatest care; and the urine should be examined for sugar.  There is often severe, deep-seated pain of a neuralgic character, with cramps in the limb, and these may persist long after a line of demarcation has formed.  The dying part loses sensibility to touch and becomes cold and shrivelled.

All the physical appearances and clinical symptoms associated with dry gangrene supervene, and the dead portion is delimited by a line of demarcation.  If this forms slowly and irregularly it indicates a very unsatisfactory condition of the circulation; while, if it forms quickly and decidedly, the presumption is that the circulation in the parts above is fairly good.  The separation of the dead part is always attended with the risk of infection taking place, and should this occur, the temperature rises and other evidences of toxaemia appear.

Prophylaxis.—­The toes and feet of old people, the condition of whose circulation predisposes them to gangrene, should be protected from slight injuries such as may be received while paring nails, cutting corns, or wearing ill-fitting boots.  The patient should also be warned of the risk of exposure to cold, the use of hot-bottles, and of placing the feet near a fire.  Attempts have been made to improve the peripheral circulation by establishing an anastomosis between the main artery of a limb and its companion vein, so that arterial blood may reach the peripheral capillaries—­reversal of the circulation—­but the clinical results have proved disappointing. (See Op.  Surg., p. 29.)