276 DISEASES OF THE BRAIN. 



pendent on certain disturbances of nutrition in the capillaries, is more 

 of an independent disease than the other forms ; it closely resembles 

 the inflammatory processes, and may be ranked with the inflammations 

 of the skin that cause serous blebs. This view is supported by an in- 

 teresting observation of Hoppe^ who, on examining the fluid from a 

 chronic hydrocephalus, found it differently constituted from the normal 

 cerebro-spinal fluid, particularly that it contained more albumen. This 

 form of hydrocephalus occurs chiefly among children, and, when seen 

 later in life, it almost always dates from childhood. 



We must mention, as a peculiar variety of the disease, hydrocepha- 

 lus ex vacua, which develops as a necessary result of diminution of the 

 size of the brain, whether from general, especially senile, involution 

 (hydrocephalus senilis), or from partial atrophy of the brain. 



ANATOMICAL APPEARANCES. The amount of fluid effused into the 

 arachnoid sac is difficult to decide, since, on removing the brain from 

 the skull, the fluid from the subarachnoid space is always mixed with 

 it ; but, as we have before said, it never becomes considerable. 



The fluid effused in the subarachnoid space is sometimes regularly, 

 sometimes irregularly spread over the surface of the brain ; in the latter 

 case the arachnoid often forms a vibrating sac filled with serum. When 

 slight, cedema of the brain shows itself by the moist lustre of the cut 

 surface ; when more decided, the coherence of the brain is decreased, 

 and, if we press on some part, the resulting pit is filled with liquid 

 after a time. When of very high grade, the brain-substance is broken 

 down by the cedema, and changed to a thin white pulp (hydrocephalic 

 softening). 



In acute hydrocephalus internus the fluid effused into the ventricle 

 rarely exceeds half an ounce or an ounce ; it is either clear, or, as is 

 usually the case, slightly clouded by a scanty admixture of cast-off 

 epithelium, flocculent clots, and fragments of the surrounding brain- 

 substance. The walls of the ventricle, especially the septum, fornix, and 

 commissures, are in a state of hydrocephalic softening. 



In chronic hydrocephalus internus we generally find the ventricles 

 considerably dilated : they may contain ten or twelve ounces of fluid, 

 which is usually clear. The ependyma of the cerebral cavities is thick- 

 ened and often strewn with fine granulations. The surrounding brain- 

 substance is also more dense and tough. 



SYMPTOMS AND COURSE. Of course, the cavity of the skull is as 

 much encroached on by serous effusions as by extravasations of blood 

 or products of inflammation. As a necessary result of this, we have 

 mentioned obstruction to the entrance of arterial blood, and have given 

 attacks of convulsions and loss of consciousness as the symptoms of 

 complete and sudden arterial anaemia ; general symptoms of irritation 



