being dorsiflexed by the unopposed extensors. The depth of the track
being so disproportionate to its superficial area, the condition closely
simulates a tuberculous sinus, for which it is liable to be mistaken.
The raw surface is absolutely insensitive, so that the probe can be
freely employed without the patient even being aware of it or suffering
the least discomfort--a significant fact in diagnosis. The cavity is
filled with effete and decomposing epidermis, which has a most offensive
odour. The chronic and intractable character of the ulcer is due to
interference with the trophic nerve-supply of the parts, and to the fact
that the epithelium of the skin grows in and lines the track leading
down to the deepest part of the ulcer and so prevents closure. While
they are commonest on the sole of the foot and other parts subjected to
pressure, perforating ulcers are met with on the sides and dorsum of the
foot and toes, on the hands, and on other parts where no pressure has
been exerted.

The _tuberculous ulcer_, so often seen in the neck, in the vicinity of
joints, or over the ribs and sternum, usually results from the bursting
through the skin of a tuberculous abscess. The base is soft, pale, and
covered with feeble granulations and grey shreddy sloughs. The edges are
of a dull blue or purple colour, and gradually thin out towards their
free margins, and in addition are characteristically undermined, so that
a probe can be passed for some distance between the floor of the ulcer
and the thinned-out edges. Thin, devitalised tags of skin often stretch
from side to side of the ulcer. The outline is irregular; small
perforations often occur through the skin, and a thin, watery discharge,
containing grey shreds of tuberculous debris, escapes.

_Bazin's Disease._--This term is applied to an affection of the skin and
subcutaneous tissue which bears certain resemblances to tuberculosis. It