198 DISEASES OF THE BRAIN. 



that comes on suddenly, and quickly attains a high grade, differ from 

 those due to one which comes on slowly and is less severe. In the 

 former case the patients become dizzy ; every thing appears dark be- 

 fore them; they become insensible to impressions and incapable of 

 movement; then* pupils dilate, their respiration becomes slow, and 

 they lose consciousness ; they sink to the ground, usually with slight 

 spasms. In most cases the patients come out of this fainting-fit in a 

 short time; in other cases, usually termed apoplexia nervosa, con- 

 sciousness does not return, the swoon ends in death. Anaemia of the 

 brain artificially induced in animals by free bleeding, or by ligation of 

 all the arteries supplying the brain, has just the same symptoms ; only 

 the convulsions are usually more severe and more prominent than in 

 persons whose brain has suddenly become anaemic. The symptoms of 

 paralysis in sudden, extensive ansemia of the brain are more easily ex- 

 plained than are the convulsions. The former unmistakably depend 

 on the arrested supply of oxygen to the brain. It is known that liga- 

 tion of the abdominal aorta immediately induces paralysis of the lower 

 half of the body, whose nerves are thus deprived of arterial blood. 

 But how shall we explain the convulsions? Henle thinks that in 

 anaemia of the brain the blood from the venous plexuses of the spinal 

 marrow and the cerebro-spinal fluid from the spinal canal press toward 

 tne brain, and that the medulla oblongata and parts at the base of the 

 brain are thus thrown into a state of excitement. But J&issmaul and 

 Tenner, after ligating the afferent vessels, found not only the greater 

 hemispheres, but also the medulla oblongata, bloodless ; hence the 

 convulsions cannot be referred to congestion of the medulla. But it 

 is just as remarkable, and as contrary to all experience, to suppose 

 that there should be increased excitement of the nerve-filaments and 

 ganglion-cells, with consequent convulsions, from absolute anaemia. 

 Eiissmaul and Tenner distinctly state that, on autopsy of animals 

 whose cerebral arteries had been ligated, the arteries at the base of 

 the brain contained a " slight amount of blood," while all others were 

 found " entirely empty ; " this observation gives a small point on 

 which to hang an explanation. For we might suppose that the liga- 

 tion of those vessels caused absolute anaemia in the greater hemi- 

 spheres and their consequent paralysis, but (from the anastomosis of 

 the cerebral and spinal arteries) in the parts at the base of the brain 

 it only induced oligaemia and consequent morbid excitement. 



In anaemia of the brain that comes on slowly, just as in hyperaemia, 

 at first there are usually symptoms of irritation, subsequently those of 

 paralysis. To explain this correspondence, the hypothesis has been 

 advanced that a certain tension of the molecules of the brain is neces- 

 sary for its normal activity and that an increase or diminution of this 



