DISEASES OF THE BRAIN. 



actual headache, often accompanied by dizziness and an extraordi- 

 nary susceptibility of the special senses. There is a buzzing in the 

 ears, and a dazzling light before the eyes. This latter usually be- 

 gins at a spot in the eccentric field of vision, with a quivering as 

 though smoke were rising. It advances to the middle of the field, 

 obscuring the whole, and renders accurate seeing impossible. The 

 part first affected begins to clear, and in half an hour all is over. 

 The arteries of the eyeball are branches of the internal carotid, and 

 would naturally participate in an intracranial hypersemia. Hence, 

 in an obscure case the ophthalmoscope should aid us.] 



Hyperaemia of the brain is marked partly by symptoms of increased 

 excitability of the nerve-filaments and ganglion-cells and by their mor- 

 bid excitement (symptoms of irritation), partly by symptoms of dimin- 

 ished or lost excitability of these nerve-elements (symptoms of depres- 

 sion). Usually the symptoms of irritation precede those of depression, 

 in other cases the former do not occur, and the latter begin from the 

 outset. It is commonly supposed that this difference of symptoms 

 depends on difference of pressure on the brain from the more or less 

 distended blood-vessels, and reference is made to the analogous action 

 of the peripheral nerves, which are also irritated by a moderate pressure 

 and paralyzed by a stronger one. This explanation appears very suit- 

 able as regards the symptoms of irritation. Experience shows that 

 nerves, passing through bony canals in company with blood-vessels, 

 are thrown into a state of increased excitability and morbid excite- 

 ment by overfilling of these vessels ; the nerve-elements of the brain, 

 enclosed by the dura mater and skull, are in a like condition when the 

 cerebral vessels are overfilled. On the other hand, the reference of 

 the symptoms of paralysis to an increase of the " intra vascular pres- 

 sure " appears to me erroneous, for even in the severest forms of hy- 

 peraemia this pressure does not nearly approach the grade necessary 

 to induce paralysis of a peripheral nerve. In support of the above 

 view, it has been said that paralysis is also caused by the scarcely 

 greater " extravascular pressure " of small extravasations on the brain ; 

 but I shall hereafter show that the apoplectic symptoms from cerebral 

 haemorrhage do not depend on contusion of the brain from the extrav 

 asation. It is much more probable that the symptoms of depression 

 and paralysis arise because the requisite supply of arterial, oxygenated 

 blood to the nerve-filaments and ganglion-cells of the brain is limited 

 or entirely stopped in excessive cerebral hyperaemia. In congestive 

 hyperaemia the escape of venous blood from the brain is checked ; and 

 it is evident that, when the veins finally become filled to a certain 

 point, no new arterial blood can enter the capillaries. It is often as- 

 serted that the symptoms of cerebral hyperaemia are very similar to 01 



