d arterial resistance, and passive when it accumulates in the
vessels of the brain, owing to some obstacle to its return by the veins.

_Causes._--Active cerebral congestion may be from hypertrophy of the
left ventricle of the heart, excessive exertion, the influence of
extreme heat, sudden and great excitement, artificial stimulants, etc.
Passive congestion may be produced by any mechanical obstruction which
prevents the proper return of blood through the veins to the heart, such
as a small or ill-fitting collar, which often impedes the blood current,
tumors or abscesses pressing on the vein in its course, and organic
lesions of the heart with regurgitation.

Extremely fat animals with short, thick necks are peculiarly subject to
attacks of cerebral congestion. Simple congestion, however, is merely a
functional affection, and in a slight or moderate degree involves no
immediate danger. Extreme engorgement, on the contrary, may be followed
by rupture of previously weakened arteries and capillaries and cause
immediate death, designated then as a stroke of apoplexy.

_Symptoms._--Congestion of the brain is usually sudden in its
manifestation and of short duration. The animal may stop very suddenly
and shake its head or stand quietly braced, then stagger, make a plunge,
and fall. The eyes are staring, breathing hurried and stertorous, and
the nostrils widely dilated. This may be followed by coma, violent
convulsive movements, and death. Generally, however, the animal gains
relief in a short time, but may remain weak and giddy for several days.
If it is due to organic change of the heart or the disease of the blood
vessels in the brain, then the symptoms may be of slow development,
manifested by drowsiness, dimness or imperfect vision, difficulty in
voluntary movements, diminished sensibility of the skin, loss of
consciousness, delirium, and death. In milder cases effusion may take
place in the arachnoid spaces and ventricles of the brain, followed by
paralysis and other complications.

_Pathology._--In congestion of the brain the cerebral vessels are loaded
with blood, the venous sinuses distended to an extreme degree, and the
pressure exerted upon the brain constitutes actual compression, giving
rise to the symptoms just mentioned. On post-mortem examinations this
engorgement is found universal throughout the brain and its membranes,
which serves to distinguish it from inflammations of these structures,
in which the en