Treatment.—­The general treatment of embolic gangrene is the same as that for the senile form.  Success has followed opening the artery and removing the embolus.  The artery is exposed at the seat of impaction and, having been clamped above and below, a longitudinal opening 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 bacteria, dries up, and the shrivelled brown skin is slowly separated by the growth of granulation tissue beneath and around it.

Fingers, toes, or even considerable portions of limbs may in the same way be suddenly destroyed by severe trauma, and undergo mummification.  If organisms gain access, typical moist gangrene may ensue, or changes similar to those of ordinary post-mortem decomposition may take place.