212 DISEASES OF THE BRAIN. 



tomatology of brain-diseases .confined to certain points. I have already 

 remarked that the variation of symptoms, the temporary improvement 

 or exacerbation, observed in the course of some brain-diseases, depend 

 greatly on the increase or decrease of the collateral oedema about the 

 point of disease. 



The third form of partial anaemia of the brain, the result of com- 

 pression of the capillaries of portions of the brain from diseases caus- 

 ing pressure, induces constant and characteristic symptoms, which of 

 course vary according as the anaemia is in one of the greater hemi- 

 spheres or is below the tentorium. If the capillaries of one of the 

 greater hemispheres be compressed by an effusion of blood, by a 

 tumor, or any other local disease contracting the space in the skull, 

 there will be hemiplegia, no matter where the said disease be located. 

 This hemiplegia is limited to the lower half of the face, and to the 

 two extremities of the opposite side. It has often been considered as 

 enigmatical, that in many cases diseases above or below one of the 

 greater hemispheres, as well as within it, led to hemiplegia, while in 

 other cases the same diseases at the base, convexity, or in the medulla 

 of a great hemisphere did not induce hemiplegia; and tables have 

 been made out which show at a glance this want of correspondence. 

 I consider these tables as utterly worthless, unless the variety of the 

 disease be stated in them ; and I think it very important to distinguish 

 between two classes of disease, whose effect is very different ; namely, 

 those which occupy more space than the brain-filaments and ganglion- 

 cells which they supplant, and those which do not. Diseases at the 

 base, convexity, or in the medullary portion of the cerebrum only in 

 duce hemiplegia when they lessen the space, in other cases they do 

 not cause it (unless collateral oedema in their vicinity extend to the 

 thalamus and corpus striatum). There are exceptional cases where 

 hemiplegia does not occur in disease of one of the greater hemisphere? 

 whose products certainly contract the space. When tumors grow 

 very slowly the brain usually atrophies, and as much space may be 

 gained in the skull by the disappearance of brain-substance as is lost 

 by the slow growth of the tumor. In such cases there is no anaemia 

 of the affected hemisphere from compression of the capillaries, and 

 consequently, if the tumor be not in the immediate vicinity of the 

 corpus striatum and thalamus, hemiplegia does not occur. We must 

 also remember the extensive communication between the two uppei 

 chambers of the skull at then- anterior part. It is evident that at tmY 

 place pressure on one hemisphere may more readily be propagated tc 

 the other than at any other part. But, the more pressure is divided 

 up, the weaker its action becomes. In accordance with these consid- 

 erations, diseases of the anterior lobes, which do not encroach too much 



