tuberculous abscess may in one or other of these ways be a cause of
death.

_Residual abscess_ is the name given to an abscess that makes its
appearance months, or even years, after the apparent cure of tuberculous
disease--as, for example, in the hip-joint or spine. It is called
residual because it has its origin in the remains of the original
disease.

[Illustration: FIG. 34.--Tuberculous Abscess in right lumbar region in a
woman aged thirty.]

#Diagnosis.#--A cold abscess is to be diagnosed from a syphilitic gumma,
a cyst, and from lipoma and other soft tumours. The differential
diagnosis of these affections will be considered later; it is often made
easier by recognising the presence of a lesion that is likely to cause a
cold abscess, such as tuberculous disease of the spine or of the
sacro-iliac joint. When it is about to burst externally, it may be
difficult to distinguish a tuberculous abscess from one due to infection
with pyogenic organisms. Even when the abscess is opened, the
appearances of the pus may not supply the desired information, and it
may be necessary to submit it to bacteriological examination. When the
pus is found to be sterile, it is usually safe to assume that the
condition is tuberculous, as in other forms of suppuration the causative
organisms can usually be recognised. Experimental inoculation will
establish a definite diagnosis, but it implies a delay of two to three
weeks.

#Treatment.#--The tuberculous abscess may recede and disappear under
general treatment. Many surgeons advise that so long as the abscess is
quiescent it should be left alone. All agree, however, that if it shows
a tendency to spread, to increase in size, or to approach the skin or a
mucous membrane, something should be done to avoid the danger of its
bursting and becoming infected with pyogenic organisms. Simple
evacuation of the abscess by a hollow needle may suffice, or bismuth or
iodoform may be introduced after withdrawal of the contents.

_Evacuation of the Abscess and Injection of Iodoform._--The iodoform is
employed in the form of a 10 per cent. solution in ether or the same
proportion suspended in glycerin. Either form becomes sterile soon after
it is prepared. Its curative effects would appear to depend upon the
liberation of iodine, which restrains the activity of the bacilli, and
upon its capacity for irritating the tissues and so inducing a
protective leucocytosis, and also of stimulating the formati