gangrene_; _Gangrene associated with spasm of
blood vessels_; _Raynaud's disease_; _Angio-sclerotic gangrene_;
_Gangrene from ergot_. Bacterial varieties of gangrene.
_Pathology_--clinical varieties--_Acute infective gangrene_;
_Malignant oedema_; _Acute emphysematous_ or _gas gangrene_;
_Cancrum oris_, _etc_. Bed-sores: _Acute_; _chronic_.

Gangrene or mortification is the process by which a portion of tissue
dies _en masse_, as distinguished from the molecular or cellular death
which constitutes ulceration. The dead portion is known as a _slough_.

In this chapter we shall confine our attention to the process as it
affects the limbs and superficial parts, leaving gangrene of the viscera
to be described in regional surgery.

TYPES OF GANGRENE

Two distinct types of gangrene are met with, which, from their most
obvious point of difference, are known respectively as _dry_ and
_moist_, and there are several clinical varieties of each type.

Speaking generally, it may be said that dry gangrene is essentially due
to a simple _interference with the blood supply_ of a part; while the
main factor in the production of moist gangrene is _bacterial
infection_.

The cardinal signs of gangrene are: change in the colour of the part,
coldness, loss of sensation and motor power, and, lastly, loss of
pulsation in the arteries.

#Dry Gangrene# or #Mummification# is a comparatively slow form of local
death due, as a rule, to a diminution in the arterial blood supply of
the affected part, resulting from such causes as the gradual narrowing
of the lumen of the arteries by disease of their coats, or the blocking
of the main vessel by an embolus.

As the fluids in the tissues are lost by evaporation the part becomes
dry and shrivelled, and as the skin is usually intact, infection does
not take place, or if it does, the want of moisture renders the part an
unsuitable soil, and the organisms do not readily find a footing. Any
spread of the process that may take place is chiefly influenced by the
anatomical distribution of the blocked arteries, and is arrested as soon
as it reaches an area rich in anastomotic vessels. The dead portion is
then cast off, the irritation resulting from the contact of the dead
with the still living tissue inducing the formation of granulations on
the proximal side of the junction, and these by slowly eating into the
dead portion produce a furrow--the _line of demarcation_--which
grad