on. If, on the other hand, there is
fear of a mixed infection, especially in abscesses near the rectum or
anus, it is safer to treat it by the open method, packing the cavity
with iodoform worsted or bismuth gauze, which is renewed at intervals of
a week or ten days as the cavity heals from the bottom.

Another method is to incise the abscess, cleanse the cavity with gauze,
irrigate with Carrel-Dakin solution and pack with gauze smeared with the
dilute non-toxic B.I.P.P. (bismuth and iodoform 2 parts, vaseline 12
parts, hard paraffin, sufficient to give the consistence of butter). The
wound is closed with "bipped" silk sutures; one of these--the "waiting
suture"--is left loose to permit of withdrawal of the gauze after
forty-eight hours; the waiting suture is then tied, and delayed primary
union is thus effected.

When the skin over the abscess is red, thin, and about to give way, as
is frequently the case when the abscess is situated in the subcutaneous
cellular tissue, any skin which is undermined and infected with tubercle
should be removed with the scissors at the same time that the abscess is
dealt with.

In abscesses treated by the open method, when the cavity has become
lined with healthy granulations, it may be closed by secondary suture,
or, if the granulating surface is flush with the skin, healing may be
hastened by skin-grafting.

If the tuberculous abscess has burst and left a _sinus_, this is apt to
persist because of the presence of tuberculous tissue in its wall, and
of superadded pyogenic infection, or because it serves as an avenue for
the escape of discharge from a focus of tubercle in a bone or a lymph
gland.

[Illustration: FIG. 35.--Tuberculous Sinus injected through its opening
in the forearm with bismuth paste.

(Mr. Pirie Watson's case--Radiogram by Dr. Hope Fowler.)]

The treatment varies with the conditions present, and must include
measures directed to the lesion from which the sinus has originated. The
extent and direction of any given sinus may be demonstrated by the use
of the probe, or, more accurately, by injecting the sinus with a paste
consisting of white vaseline containing 10 to 30 per cent. of bismuth
subcarbonate, and following its track with the X-rays (Fig. 35).

It was found by Beck of Chicago that the injection of bismuth paste is
frequently followed by healing of the sinus, and that, if one injection
fails to bring about a cure, repeating the injection every second da