218 DISEASES OF THE HORSE. 
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 sub- 
ject 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 con- 
trary, 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 mani- 
festation 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 im- 
perfect vision, difficulty in voluntary movements, diminished sensi- 
bility 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.—tin 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 through- 
out the brain and its membranes, which serves to distinguish it from 
inflammations of these structures, in which the engorgements are 
confined more or less to circumscribed portions. A prolonged con- 
gestion may, however, lead to active inflammation, and in that case 
we find serous and plastic exudations in the cavities of the brain. In 
addition to the intensely engorged condition of the vessels we find 
the gray matter of the brain redder than natural. In cases in which 
several attacks have occurred the blood vessels are often found 
permanently dilated. 
Treatment.—The animal should be taken out of harness at once, 
with prompt removal of all mechanical obstructions to the circula- 
tion. If it is caused by venous obstruction by too tight a collar, the 
