usually has a turbid and milky
appearance.

In an acute abscess the surrounding _brain tissue_ is engorged and
infiltrated with pus; in a chronic abscess it is condensed, and the
pus may be encapsulated by the formation of a zone of young fibrous
tissue round its periphery. In this condition the abscess may remain
"latent," giving rise to no symptoms for many weeks or even months.

_Clinical features._--The _initial_ formation of pus in the cerebral
tissue is associated with the sudden onset of severe pain in the head,
shivering and well-marked cutis anserina, and vomiting of the cerebral
type. The discharge from the ear usually diminishes or may even cease.

As a _localised abscess_ develops the patient gradually passes, into a
stuporous condition; he does not lose consciousness, but, his
cerebration is slow, he seems unable to sustain his attention, for any
length of time, and he answers questions "slowly, briefly, but, as a
rule, correctly" (Macewen). The pain in the region of the ear becomes
less intense, but the mastoid and temporal areas on the affected side
are tender on percussion. The temperature falls, and, as a rule,
remains subnormal. Rigors are unusual: their occurrence usually
indicating the development of some complication such as sinus
phlebitis. The pulse is full, regular, and slow (40 to 60). Vomiting
frequently occurs, and the bowels are often obstinately constipated.

There is no actual paresis, but there is a "gradual diminution of the
ability to apply his strength." The superficial reflexes are late of
disappearing and the disturbance is unilateral. The optic discs are
moderately swollen. "The face is expressionless, passive, and cloudy.
It may assume a meaningless smile, with which the features are not
lit; it is too mechanical" (Macewen).

_Differential Diagnosis._--In the early stages it is often difficult
to distinguish between meningitis and cerebral abscess. The chief
points on which reliance is to be placed are that in meningitis the
pulse shows an irregularity, both in rate and force, which is wanting
in cases of uncomplicated abscess. In meningitis the temperature is
raised, while in abscess it is persistently subnormal. The
superficial reflexes, particularly the abdominal reflexes, disappear
early in meningitis and the disturbance is bilateral; in abscess they
are slower to disappear, and one side only is affected. Retraction of
the neck, when present, is a characteristic sign of me