DIAGNOSTIC SIGNS OF ABSCESS. 
321 
brain, until such time that some particular and decisive cause, 
operating in union with the changes occurring in the sac, its size 
or collection, gives rise to disease of the cerebral substance by 
which it is surrounded. 
Abscesses of the brain are occasionally accompanied by various 
other lesions of the cerebral substance, and then effusion, external 
or internal, of the surfaces, tumours, softening, hardening, inflam- 
matory appearances of the membranes, or ulceration in the walls of 
the cyst, are common attendants : accumulations of pus in the brain, 
like purulent matter in other organs or parts, attempt to escape 
from the body. Occasionally they make their way to the surfaces 
of the organ, either internal or external, and sometimes they break 
into the ventricles. If they open upon the periphery of the brain, 
the intervening membranes and bone are sometimes carious pre- 
vious to death, and I believe that the cribriform plate of the eth- 
moid bone has been destroyed, and the pus escaped externally 
through the nasal fossse in the human subject. There may also 
be an evacuation by the ear, procured by destruction of the petrous 
portion of the temporal bone. 
Pus found in the brain does not appear to differ from that formed 
in any other textures of the frame. It is occasionally found ex- 
ceedingly foetid. The only difference that I am aware of is, that 
it varies in colour from a dirty yellow or greenish white to one 
altogether white. 
Encysted collections of pus in the brain are evidently produced 
by inflammatory action, but of so slow a grade of intensity as to be 
analogous to the chronic form of abscess. 
Those purulent infiltrations found in the large nervous masses, 
like that which is met with in the other viscera resulting from ab- 
sorption of purulent matter into the circulation, are the product of 
morbid secretion, rather than of inflammatory action, and take 
place very rapidly. Collections of pus are most frequently ob- 
served in the hemispheres ; but suppuration may occur in any part 
of the organ, and of course produce effects varying with the extent 
of accumulation and the situation of the purulent collection. Slow 
effusions of blood, the existence of tumours, or any other diseased 
production, produce similar effects. 
Symptoms . — The symptoms of abscess in the brain are very 
similar to those of inflammation of the membranes and substance 
of the organ. I have before stated as an important pathological 
fact, that, previous to a considerable increase of the collection and 
duration of its existence from the circumstance of the slowness of 
the formation of the encysted abscess, there were no indications of 
disturbance in the functions of the cerebrum ; but, when the col- 
lection was much increased and had continued long, the nervous 
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