It is to be borne in mind that the object of amputation in these cases is merely to remove the gangrenous part, and so relieve the patient of the discomfort and the risks from infection which its presence involves.  While it is true that in many of these patients the operation is borne remarkably well, it must be borne in mind that those who suffer from senile gangrene are of necessity bad lives, and a guarded opinion should be expressed as to the prospects of survival.  The possibility of the disease developing in the other limb has already been referred to.

[Illustration:  FIG. 21.—­Embolic Gangrene of Hand and Arm.]

#Embolic Gangrene# (Fig. 21).—­This is the most typical form of gangrene resulting from the sudden occlusion of the main artery of a part, whether by the impaction of an embolus or the formation of a thrombus in its lumen, when the collateral circulation is not sufficiently free to maintain the vitality of the tissues.

There is sudden pain at the site of impaction of the embolus, and the pulses beyond are lost.  The limb becomes cold, numb, insensitive, and powerless.  It is often pale at first—­hence the term “white gangrene” sometimes applicable to the early appearances, which closely resemble those presented by the limb of a corpse.

If the part is aseptic it shrivels, and presents the ordinary features of dry gangrene.  It is liable, however, especially in the lower extremity and when the veins also are obstructed, to become infected and to assume the characters of the moist type.

The extent of the gangrene depends upon the site of impaction of the embolus, thus if the abdominal aorta becomes suddenly occluded by an embolus at its bifurcation, the obstruction of the iliacs and femorals induces symmetrical gangrene of both extremities as high as the inguinal ligaments.  When gangrene follows occlusion of the external iliac or of the femoral artery above the origin of its deep branch, the death of the limb extends as high as the middle or upper third of the thigh.  When the femoral below the origin of its deep branch or the popliteal artery is obstructed, the veins remaining pervious, the anastomosis through the profunda is sufficient to maintain the vascular supply, and gangrene does not necessarily follow.  The rupture of a popliteal aneurysm, however, by compressing the vein and the articular branches, usually determines gangrene.  When an embolus becomes impacted at the bifurcation of the popliteal, if gangrene ensues it usually spreads well up the leg.

When the axillary artery is the seat of embolic impaction, and gangrene ensues, the process usually reaches the middle of the upper arm.  Gangrene following the blocking of the brachial at its bifurcation usually extends as far as the junction of the lower and middle thirds of the forearm.

Gangrene due to thrombosis or embolism is sometimes met with in patients recovering from typhus, typhoid, or other fevers, such as that associated with child-bed.  It occurs in peripheral parts, such as the toes, fingers, nose, or ears.