circumstances, however, in which an
operation is required; for example, in disease of the lymph glands for
the removal of inert masses of caseous material, in disease of bone for
the removal of sequestra, or in disease of joints to improve the
function of the limb. It is to be understood, however, that operative
treatment must always be preceded by and combined with other therapeutic
measures.

TUBERCULOUS ABSCESS

The caseation of tuberculous granulation tissue and its liquefaction is
a slow and insidious process, and is unattended with the classical signs
of inflammation--hence the terms "cold" and "chronic" applied to the
tuberculous abscess.

In a cold abscess, such as that which results from tuberculous disease
of the vertebrae, the clinical appearances are those of a soft, fluid
swelling without heat, redness, pain, or fever. When toxic symptoms are
present, they are usually due to a mixed infection.

A tuberculous abscess results from the disintegration and liquefaction
of tuberculous granulation tissue which has undergone caseation. Fluid
and cells from the adjacent blood vessels exude into the cavity, and
lead to variations in the character of its contents. In some cases the
contents consist of a clear amber-coloured fluid, in which are suspended
fragments of caseated tissue; in others, of a white material like
cream-cheese. From the addition of a sufficient number of leucocytes,
the contents may resemble the pus of an ordinary abscess.

The wall of the abscess is lined with tuberculous granulation tissue,
the inner layers of which are undergoing caseation and disintegration,
and present a shreddy appearance; the outer layers consist of
tuberculous tissue which has not yet undergone caseation. The abscess
tends to increase in size by progressive liquefaction of the inner
layers, caseation of the outer layers, and the further invasion of the
surrounding tissues by tubercle bacilli. In this way a tuberculous
abscess is capable of indefinite extension and increase in size until it
reaches a free surface and ruptures externally. The direction in which
it spreads is influenced by the anatomical arrangement of the tissues,
and possibly to some extent by gravity, and the abscess may reach the
surface at a considerable distance from its seat of origin. The best
illustration of this is seen in the psoas abscess, which may originate
in the dorsal vertebrae, extend downwards within the sheath of the psoas
muscle,