152 THE CIRCULATION. 



Some experiments performed by Dr. Kellie appeared to estab- 

 lish the correctness of this view. But Dr. Burrows having 

 repeated these experiments, and performed additional ones, 

 obtained different results. He found that in 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 congestion of the cerebral vessels in rab- 

 bits killed by strangling 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 his head down- 

 wards, 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 diminution or increase in the quantity of the 

 cerebro-spinal fluid, which, by readily admitting of being re- 

 moved 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 bloodvessels, to which reference has 

 been made, insure 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 cir- 

 cumstances, 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 displacement 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 insuffi- 

 cient supply of blood. Hence we may consider that the cere- 

 bro-spinal fluid in the interior of the skull not only subserves 

 the mechanical functions of fat in other parts as a packing 

 material, but by the readiness with which it can be displaced 

 into the spinal canal, provides the means whereby undue pres- 

 sure and insufficient supply of blood are equally prevented. 



Circulation in Erectile Structures. The instances of greatest 

 variation in the quantity of blood contained, at different times, 

 in the same organs, are found in certain structures which, 

 under ordinary circumstances, are soft and flaccid, but, at cer- 

 tain times, receive an unusually large quantity of blood, be- 



