extends higher than that of bone and
muscle.

These facts furnish us with indications as to the seat and method of
amputation. Experience has proved that in senile gangrene of the lower
extremity the most reliable and satisfactory results are obtained by
amputating in the region of the knee, care being taken to perform the
operation so as to leave the prepatellar anastomosis intact by retaining
the patella in the anterior flap. The most satisfactory operation in
these cases is Gritti's supra-condylar amputation. Haemorrhage is easily
controlled by digital pressure, and the use of a tourniquet should be
dispensed with, as the constriction of the limb is liable to interfere
with the vitality of the flaps.

When the tibial vessels can be felt pulsating at the ankle it may be
justifiable, if the patient urgently desires it, to amputate lower than
the knee; but there is considerable risk of gangrene recurring in the
stump and necessitating a second operation.

That amputation for senile gangrene performed between the ankle and the
knee seldom succeeds, is explained by the fact that the vascular
obstruction is usually in the upper part of the posterior tibial artery,
and the operation is therefore performed through tissues with an
inadequate blood supply. It is not uncommon, indeed, on amputating above
the knee, to find even the popliteal artery plugged by a clot. This
should be removed at the amputation by squeezing the vessel from above
downward by a "milking" movement, or by "catheterising the artery" with
the aid of a cannula with a terminal aperture.

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 circulat