872 SCOTTISH METROPOLITAN VETERINARY ASSOCIATION. 
In order to carry out this design it will be necessary to illus¬ 
trate by a diagram the relationship between the sympathetic and 
cerebro-spinal system of nerves,, and by calling your attention to 
a remarkable physiological fact which was first discovered by 
Monro, jun., afterwards illustrated by Abercrombie and Dr. 
Kellie, and defended by Dr. Keid. Its accuracy lias been denied 
by some physiologists, but, so far as I am able to judge of 
evidence, the denial or disproval of the fact has not been 
established. 
The fact, which materially alfects our views of the disease 
under consideration, and also guides us in treatment, is this :— 
“That the cranial cavity can only contain a given quantity of 
matter at one time, that is, if one portion of its solid or liquid 
contents is removed or altered in position it must be replaced by 
another, as no vacuum can be formed in it, nor can the external 
air obtain entrance to the spot from whence the fluid or solid is 
displaced.” This is accounted for by the fact that the bones of 
the cranium form a solid cupola which resists atmospheric 
pressure. Hence, if we withdraw blood from the veins, the 
arteries are immediately filled to preserve the plenitude of the 
cranium, and vice versa. I have said that this is an important 
fact, inasmuch as it teaches us that once a clot is formed in the 
arteries of the brain no amount of bleeding will alter the 
quantity of fluid within the cranial cavity, as, however much 
may be abstracted from the jugular vein there will still be the 
same quantity of blood in the sinuses as before the vene¬ 
section. 
If it were possible for pressure to be exerted on the blood¬ 
vessels of the brain it could only act upon the arteries, because 
of the peculiarity of the venous circulation, and we frequently 
find that the walls of the sinuses are absolutely incompressible—- 
from the development of hard material, as cartilage, &c., 
within their structures—by any force which excited or increased 
circulation could bring to bear upon them. 
Causes. —In considering the causes it will be necessary to 
divide them into remote , or predisposing; and exciting 0 or 
proximate; and further we must look upon them as centric , or 
those exerted directly upon the brain or spinal cord, as conges^ 
tion, the formation of clots of blood, diseased condition of the 
blood, &c., producing true apoplexy; and eccentric , or those 
which act by reflex nervous irritation, producing, more properly 
speaking, convulsions. These causes may be in existence singly 
or may co-exist. 
1st. Predisposing Causes. —Or those which are in existence for 
some time prior to parturition, and which only indirectly affect 
the ultimate invasion of the disease. Some of them may also be 
