fected
area is hot, the redness of inflammation gives place to a dusky purple
colour, with a pale, sometimes yellow, spot where the pus is near the
surface. The swelling increases in size, the firm brawny centre becomes
soft, projects as a cone beyond the level of the rest of the swollen
area, and is usually surrounded by a zone of induration.

By gently palpating with the finger-tips over the softened area, a fluid
wave may be detected--_fluctuation_--and when present this is a certain
indication of the existence of fluid in the swelling. Its recognition,
however, is by no means easy, and various fallacies are to be guarded
against in applying this test clinically. When, for example, the walls
of the abscess are thick and rigid, or when its contents are under
excessive tension, the fluid wave cannot be elicited. On the other hand,
a sensation closely resembling fluctuation may often be recognised in
oedematous tissues, in certain soft, solid tumours such as fatty tumours
or vascular sarcomata, in aneurysm, and in a muscle when it is palpated
in its transverse axis.

When pus has formed in deeper parts, and before it has reached the
surface, oedema of the overlying skin is frequently present, and the skin
pits on pressure.

With the formation of pus the continuous burning or boring pain of
inflammation assumes a throbbing character, with occasional sharp,
lancinating twinges. Should doubt remain as to the presence of pus,
recourse may be had to the use of an exploring needle.

_Differential Diagnosis of Acute Abscess._--A practical difficulty which
frequently arises is to decide whether or not pus has actually formed.
It may be accepted as a working rule in practice that when an acute
inflammation has lasted for four or five days without showing signs of
abatement, suppuration has almost certainly occurred. In deep-seated
suppuration, marked oedema of the skin and the occurrence of rigors and
sweating may be taken to indicate the formation of pus.

There are cases on record where rapidly growing sarcomatous and
angiomatous tumours, aneurysms, and the bruises that occur in
haemophylics, have been mistaken for acute abscesses and incised, with
disastrous results.

#Treatment of Acute Abscesses.#--The dictum of John Bell, "Where there
is pus, let it out," summarises the treatment of abscess. The extent and
situation of the incision and the means taken to drain the cavity,
however, vary with the nature, site, and rel