180 DISEASES OF THE BRAIN. 



surface of the brain as a means of determining the amount of blood 

 contained in the cerebral vessels. I do not deny that this sign has 

 some value, particularly in judging of passive cerebral hyperaemia; 

 but I must add that the size and number of these drops of blood de- 

 pend far more on the fluidity of the blood than on the fulness of the 

 vessels. At all events, in cases where there can be no doubt of death 

 having resulted from increased flow of blood to the head, or from its 

 obstructed escape thence, on a section through the brain, its substance 

 is often found very pale, and on its cut surface only a few small blood- 

 drops ooze up. This circumstance, and the symptoms of paralysis 

 occurring in the severer cases of cerebral hyperaemia (of which we shall 

 speak more fully in the next paragraph), cause it to appear to me very 

 probable that, when there is increased lateral pressure in the small 

 arteries and veins of the brain, a transudation of serum from them 

 into the perivascular spaces and interstices of the brain may very 

 readily take place, and cause compression of the capillaries. It is only 

 in yielding and distensible organs and tissues, which are not enclosed 

 by firm envelopes, that any considerable cedema can coexist with a 

 normal fulness of the capillaries. In all tissues enclosed by fascia or 

 other firm capsule, cedema causes anaemia of the capillaries. If the 

 size of the brain be not diminished by atrophy, and if the skull be 

 closed, or, it remaining opened, if the dura mater be tense, there is no 

 doubt that a sh'ght transudation of serum will suffice to completely 

 compress the capillaries of the brain. It is true, we cannot be sure, 

 from post-mortem examination, that there is such a secondary cedema ; 

 but the supposition that such is the case appears to us perfectly justi- 

 fiable when a patient has died with the symptoms of cerebral paralysis, 

 and if, on autopsy, we find that the very white hue of the brain-sub- 

 stance and the slight number of small blood-points appearing on its 

 cut surface contrast strongly with the distention of the large vessels 

 in the meninges. 



Where the hyperaemia is often repeated, atrophy of the brain and 

 decided dilatation of the vessels result. The vessels of the meninges, 

 which are unmistakably dilated, run a tortuous course; on section 

 through the brain, we may distinctly see the gaping mouths of the 

 vessels; the dilatation may even be observed in the capillaries on 

 microscopical examination. There is plenty of serum in the sub- 

 arachnoid spaces, the brain-substance is moist and shining. This ap- 

 pearance, which is frequent in topers, is readily understood, if we 

 remember that, in atrophy of the brain, the fluid contents of the skull 

 must increase so as to fill the cavity. It is doubtful whether the de- 

 velopment of the Pacchionian bodies can also be considered as a result 

 of repeated hyperaemia; they are sometimes solitary, sometimes 



