[Illustration: FIG. 20.--Senile Gangrene of the Foot, showing line of
demarcation.]
_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.
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