The size of the apoplectic clot varies c dembly (excluding the cases of capillary plexy in which no coalition has taken pl frorn the size of a millet seed to that of a in fist, tile clot sometimes breaking up the fib nervous matter of the hemisphere with its rounding grey layer, and completely occup its interior. There is no part of the b so favourable for the occurrence of a I apoplectic clot as the hemisphere, becaus softness and magnitude afford the least resist to the flux of blood.
Apoplectic effusions occur most freque in the hemispheres of the brain, affecting the corpora striata or optic thalami, and s ing from them into the white substance hemisphere, or sometimes breaking up substance and passing into the lateral ventricle of one side, and thence through the foramen of Monro into the lateral ventricle of the other side. The convolutions are the next most frequent seat of apoplexy, and after them either hemisphere of the cerebellum, and either crus cerebri. The pons, crus cerebri, crus cerebelli, are much less frequently affected by hemorrhage. These parts are denser in struc ture and less freely supplied with blood, and, therefore, less prone to apoplectic effusion than those before rnentioned.
Cancer qf the brain.—Cancer is occasion ally, although very rarely, found affecting some part of the encephalon ; most frequently it ex tends into some portion of it from the meninges. • Andral lias given a good history of this diseased condition, founded upon the analysis of forty-three cases.* Of these, the hemispheres were the seat of the cancer in thirty-one, in five the cerebellum was affected, once the meso cephale, three times the pituitary body, and three times the spinal cord.
The number and size of the cancerous tu mors are very various. The cancer may begin in the meninges, and attack the bone on the one hand and the brain on the other ; or it may be first developed in the substance of the hemisphete. When the disease is superficial the cranial walls may become extensively im plicated. I have seen the greater part of the parietal bone implicated in a cancerous tumor. Andral mentions a case in which the frontal and temporal bones were completely destroyed, and another in which the cancer, developed at the inferior surface of the brain, passed out through the foramina of the base of the cranium.
Cerebral cancer is most frequently of the soft or fungoid kind, but sometimes it occurs in the form of small hard tumours, deposited in various parts of the brain, and separated from the surrounding cerebral substance by a distinct membrane or capsule. Frequently it appears to be primary, or at least there seems ' no evident connection between it and any other cancerous deposit situate elsewhere. Of An dral's forty cases only ten were associated with cancer in other situations.
Tubercle of the brain. —The anatomical characters of tubercle of the brain are very definite. The colour is yellow, the more con spicuous by reason of the white or grey of the surrounding cerebral texture ; the consistence cheesy. Its section affords a smooth and clean surface, but if broken up by the point of the I knife, its texture appears to be minutely grunt lar. Sometimes this tubercular matter rnay be picked out of a very distinct capsule. The , tubercles vary very much in size, sometimes as I small as a millet seed, frequently the size of a split pea, or even as large as a filbert or a wal nut, rarely much larger.
I The parts of the brain most frequently af I fected by tubercle are the cerebral hemispheres land those of the cerebellum. The mesocephale and the medulla oblongata are rarely the seat of it. It is generally situated near the surface or near some process of pia mater ; conse quently it is most commonly rnet with in the grey matter of the brain.
Cerebral tubercle excites inflammation in the surrounding brain substance, which is then found in the state of red softening ; and some times suppuration may be established, the tubercular matter being more or less broken down and diffused in the pus. lt is thus that tubercles of the brain prove so destructive to life. They may remain quiescent and unde tected and even unsuspected until some irritation, often propagated from the periphery, excites surrounding inflammation, which by reason of the presence of the foreign matter of the tuber cle, is kept up, and refuses to yield to any measure of treatment. Cerebral tubercle exhi bits no spontaneous tendency to soften, nor does it frequently degenerate into earthy con cretions.