THE NERVOUS SYSTEM. 791 



ignorant. In some cases it seeins to be due to an increased arterial ten- 

 sion in such diseases of the heart as induce this change, as in the car- 

 diac hypertrophy which may accompany some forms of chronic diffuse 

 nephritis ; or it may result from unusual exertion or mental excitement. 



The most frequent seat of haemorrhage is in the corpora striata and 

 optic thalami (Fig. 518), and the brain tissue in their vicinity, and here 

 they occur most often in the parts supplied by the branches of the mid- 

 dle cerebral artery. The possibility of haemorrhage in the floor of the 

 fourth ventricle should be borne in mind in investigating cases of sud- 

 den death from obscure causes. 



Haemorrhages frequently seriously affect other portions of the brain 

 than those immediately supplied by the ruptured vessels. Thus haemor- 

 rhages in the cortical substance or beneath the pia mater may force their 

 way deep into the brain substance ; or, in haemorrhage in the brain sub- 

 stance, the blood may burst into the ventricles or work its way into the 

 iutermeningeal space, and, either at the seat of its occurrence or in the 

 situations into which it is forced, may give rise to serious compression 

 of the brain. Portions of the brain containing large extravasations may 

 be enlarged, the tissue anaemic from pressure, the convolutions flattened, 

 and the surface dry. As the blood is poured out, the brain tissue is usu- 

 ally torn and lacerated, so that the apoplectic clot usually consists of 

 detritus of brain tissue intermingled with blood. If, however, the blood 

 is poured out from a single vessel, the lacerated brain tissue may be 

 pressed aside, and the greater portion of the red mass may consist of 

 pure blood clot. 



The appearances presented by haemorrhages in the brain vary greatly, 

 depending upon the time which has elapsed since their occurrence. If 

 life continue, the oedema which usually soon occurs in the vicinity of the 

 haemorrhage disappears and the clot becomes drier and firmer ; gradually 

 the blood undergoes the usual series of changes seen in extravasation ; 

 the haemoglobin decomposes, forming granules and crystals of blood pig- 

 ment ; the blood cells and fibrin undergo degeneration and absorption ; 

 the detritus of brain tissue undergoes fatty degeneration. As these al- 

 terations occur the color changes to reddish-brown, orange, or yellow, 

 and the adjacent brain tissue may be discolored by imbibition. 



Inflammatory reaction may occur in the vicinity, leading either to the 

 formation of a more or less pigmeuted cicatrix, or to a cyst with yellow- 

 ish fluid contents and a fibrous, more or less pigmented wall. The proc- 

 ess of degeneration and absorption of the blood and broken-down brain 

 tissue, and their replacement by a cyst or by a cicatrix, is a slow one, 

 and the cysts and cicatrices may resemble those formed at the seat of 

 enibolic softening. Not infrequently we find in the brain of a person 

 dead from recent apoplexy the remains of old clots presenting some one 

 of the above-described stages of absorption. The apoplectic cysts and 

 cicatrices persist for a long time after their formation. 



Secondary degenerations (see page 809) following haemorrhages de- 

 pend entirely upon the cells destroyed or the fibre tracts interrupted. 



