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
is met with almost exclusively between the knee and the ankle, and it
usually affects both legs. It is commonest in girls of delicate
constitution, in whose family history there is evidence of a tuberculous
taint. The patient often presents other lesions of a tuberculous
character, notably enlarged cervical glands, and phlyctenular
ophthalmia. The tubercle bacillus has rarely been found, but we have
always observed characteristic epithelioid cells and giant cells in
sections made from the edge or floor of the ulcer.

[Illustration: FIG. 16.--Bazin's Disease in a girl aet. 16.]

The condition begins by the formation in the skin and subcutaneous
tissue of dusky or livid nodules of induration, which soften and
ulcerate, forming small open sores with ragged and undermined edges, not
unlike thos