is made
and the clot carefully extracted with the aid of forceps; it is
sometimes unexpectedly long (one recorded from the femoral artery
measured nearly 34 inches); the wound in the artery is then sewn up with
fine silk soaked in paraffin. When amputation is indicated, it must be
performed sufficiently high to ensure a free vascular supply to the
flaps.

#Gangrene following Ligation of Arteries.#--After the ligation of an
artery in its continuity--for example, in the treatment of aneurysm--the
limb may for some days remain in a condition verging on gangrene, the
distal parts being cold, devoid of sensation, and powerless. As the
collateral circulation is established, the vitality of the tissues is
gradually restored and these symptoms pass off. In some cases,
however,--and especially in the lower extremity--gangrene ensues and
presents the same characters as those resulting from embolism. It tends
to be of the dry type. The occlusion of the vein as well as the artery
is not found to increase the risk of gangrene.

#Gangrene from Mechanical Constriction of the Vessels of the part.#--The
application of a bandage or plaster-of-Paris case too tightly, or of a
tourniquet for too long a time, has been known to lead to death of the
part beyond; but such cases are rare, as are also those due to the
pressure of a fractured bone or of a tumour on a large artery or vein.
When gangrene occurs from such causes, it tends to be of the moist type.

Much commoner is it to meet with localised areas of necrosis due to the
excessive _pressure of splints_ over bony prominences, such as the
lateral malleolus, the medial condyle of the humerus, or femur, or over
the dorsum of the foot. This is especially liable to occur when the
nutrition of the skin is depressed by any interference with its
nerve-supply, such as follows injuries to the spine or peripheral
nerves, disease of the brain, or acute anterior poliomyelitis. When the
splint is removed the skin pressed upon is found to be of a pale yellow
or grey colour, and is surrounded by a ring of hyperaemia. If protected
from infection, the clinical course is that of dry gangrene.

Bed-sores, which are closely allied to pressure sores, will be described
at the end of this chapter.

When a localised portion of tissue, for example, a piece of skin, is so
severely _crushed_ or _bruised_ that its blood vessels are occluded and
its structure destroyed, it dies, and, if not infected with bacteri