CIRCULATION IN THE BRAIN. 193 



animals bled to death, without any aperture being made 

 in the cranium, the brain became pale and anaemic like 

 other parts. And in proof that, during life, the cerebral 

 circulation is influenced by the same general circumstances 

 that influence the circulation elsewhere, he found con- 

 gestion of the cerebral vessels in rabbits killed by strang- 

 ling or drowning ; while in others, killed by prussic acid, 

 he observed that the quantity of blood in the cavity of the 

 cranium was determined by the position in which the 

 animal was placed after death, the cerebral vessels being 

 congested when the animal was suspended with its head 

 downwards, and comparatively empty when the animal 

 was kept suspended by the ears. He concluded, therefore, 

 that although the total volume of the contents of the 

 cranium is probably nearly always the same, yet the 

 quantity of blood in it is liable to variation, its increase or 

 diminution being accompanied by a simultaneous diminu- 

 tion or increase in the quantity of the cerebro-spinal fluid, 

 which, by readily admitting of being removed from one 

 part of the brain and spinal cord to another, and of being 

 rapidly absorbed, and as readily effused, would serve as 

 a kind of supplemental fluid to the other contents of the 

 cranium, to keep it uniformly filled in case of variations in 

 their quantity. And there can be no doubt that, although 

 the arrangements of the blood-vessels, to which reference 

 has been made, ensure to the brain an amount of blood 

 which is tolerably uniform, yet, inasmuch as with every 

 beat of the heart and every act of respiration, and under 

 many other circumstances, -the quantity of blood in the 

 cavity of the cranium is constantly varying, it is plain that, 

 were there not provision made for the possible displace- 

 ment of some of the contents of the unyielding bony 

 case in which the brain is contained, there would be often 

 alternations of excessive pressure with insufficient supply of 

 blood. Hence we may consider that the cerebro-spinal 

 fluid not only subserves the mechanical functions of fat in 



