ON THE COAGULATION OF -THE BLOOD sO) 
view was that exposure to the air was the essential cause of coagulation. Mr. 
Hewson believed that this was, at all events, an important element in the causes 
of the phenomenon; and many eminent physiologists and pathologists have 
held the same view, except that, instead of the air as a whole, the oxygen of 
the air has been supposed to be the important element. 
Sir Charles Scudamore considered that coagulation was greatly promoted 
by the escape of carbonic acid; and more recently the evolution of ammonia 
has been regarded as the essential cause of the change. According to the 
ammonia theory, due to Dr. Richardson of this city, the fluidity of the blood 
within the body depends on a certain amount of free ammonia holding the 
fibrine in solution, and the coagulation of the blood when withdrawn from the 
vessels is the result of the escape of the volatile alkali. 
Then, as to vital theories. These have been held by many physiologists, 
among whom may be mentioned Sir Astley Cooper and Mr. Thackrah, who, 
from experiments which they performed, were led to the inference that the 
living vessels exert an active influence upon the blood, by which coagulation 
is prevented ; and Mr. Thackrah went so far as to attribute this action of the 
vessels to nervous influence. The view that the blood is kept fluid by the 
operation of its natural receptacles has been advocated more recently by Briicke 
of Vienna, whose essay will be found in the British and Foreign Medical Review 
for 1857. Briicke performed his experiments on turtles and frogs, in which 
animals the blood remains fluid in the heart for days after death ; and I feel 
bound to say that some of the facts which he has brought forward seem to me 
quite sufficient to show that the ammonia theory, whatever amount of truth 
it may contain, cannot be the whole truth, and cannot explain the fluidity of 
the blood within the body. For example, Briicke found that, having shed 
blood from the heart of a living turtle into a basin, and transferred, with a 
syringe, a portion of that blood into the empty heart of another turtle just 
killed, the blood thus transferred into the empty heart remained fluid for hours, 
whereas that which was left in the basin coagulated in a few minutes. He 
also found that blood continued fluid in the heart of a turtle long after the 
injection of air into the heart through a vein till the cavities of the organ con- 
tained a foamy mixture of blood and air. 
Yet it by no means follows that the vital theory and the ammonia theory 
are necessarily altogether inconsistent. It might be true for anything we could 
tell, a priort, that the coagulation of the blood, when shed from the body, might 
depend on the evolution of a certain amount of ammonia, previously holding 
the fibrine in solution, and yet it might, at the same time, be true that the cause 
of the ammonia remaining in the blood in the healthy vessels might be an action 
