ually deepens until complete separation is effected. As the muscles
and bones have a richer blood supply than the integument, the death of
skin and subcutaneous tissues extends higher than that of muscles and
bone, with the result that the stump left after spontaneous separation
is conical, the end of the bone projecting beyond the soft parts.

_Clinical Features._--The part undergoing mortification becomes colder
than normal, the temperature falling to that of the surrounding
atmosphere. In many instances, but not in all, the onset of the process
is accompanied by severe neuralgic pain in the part, probably due to
anaemia of the nerves, to neuritis, or to the irritation of the exposed
axis cylinders by the dead and dying tissues around them. This pain soon
ceases and gives place to a complete loss of sensation. The dead part
becomes dry, horny, shrivelled, and semi-transparent--at first of a dark
brown, but finally of a black colour, from the dissemination of blood
pigment throughout the tissues. There is no putrefaction, and therefore
no putrid odour; and the condition being non-infective, there is not
necessarily any constitutional disturbance. In itself, therefore, dry
gangrene does not involve immediate risk to life; the danger lies in the
fact that the breach of surface at the line of demarcation furnishes a
possible means of entrance for bacteria, which may lead to infective
complications.

#Moist Gangrene# is an acute process, the dead part retaining its fluids
and so affording a favourable soil for the development of bacteria. The
action of the organisms and their toxins on the adjacent tissues leads
to a rapid and wide spread of the process. The skin becomes moist and
macerated, and bullae, containing dark-coloured fluid or gases, form
under the epidermis. The putrefactive gases evolved cause the skin to
become emphysematous and crepitant and produce an offensive odour. The
tissues assume a greenish-black colour from the formation in them of a
sulphide of iron resulting from decomposition of the blood pigment.
Under certain conditions the dead part may undergo changes resembling
more closely those of ordinary post-mortem decomposition. Owing to its
nature the spread of the gangrene is seldom arrested by the natural
protective processes, and it usually continues until the condition
proves fatal from the absorption of toxins into the circulation.

The _clinical features_ vary in the different varieties of moist