196 



diminished 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 due to 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 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 con- 

 trarj^ may be followed by rux)ture 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 his head or stand quietly braced on his legs, 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, how- 

 ever, the animal gains relief in a short time, but he may remain weak 

 and giddy for several days. If it is due to organic change of the 

 heart or to disease of the blood-vessels in the brain, then the s^'mp- 

 toms may be of slow development manifested by drowsiness, dimness 

 or imperfect vision, dif&culty in voluntary movements, diminished 

 sensibilitj'^ of the skin, loss of consciousness, delirium, and death. In 

 milder cases effusion may take j^lace 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, and 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 pos/- 

 rnortein examinations this engorgement is found universal through- 

 out the brain and its membranes, which serves to distinguisli it from 

 inflammations of these structures, in Avhich tlie engorgements are 

 confined more or less to circumscribed portions. A prolonged conges- 

 tion may, however, lead to active inflammation, and in that case we 

 will 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 in color than natural. In 

 cases where several attacks have occurred the blood-vessels are often 

 found permanently dilated. 



