756 
COAGULATION OF THE BLOOD. 
the other had only been subjected to the action of the wall 
of the tube. 
The same principle may be illustrated by an exceedingly 
simple experiment, which I performed only this very day. 
Receiving blood from the throat of a bullock into two similar 
wide-mouthed bottles, I immediately stirred one of them with 
a clean ivory rod for ten seconds very gently, so as to avoid 
the introduction of any air, and then left both undisturbed. 
At the end of a certain number of minutes, I found that, 
while the blood which had not been disturbed could be poured 
out as a fluid, with the exception of a thin layer of clot on the 
surface and an incrustation on the interior of the vessel, the 
blood in the other vessel, which had been stirred for so brief 
a period, was already a solid mass. 
I have only lately been aware of the great influence exerted 
upon the blood by exposure for a very short time to a foreign 
solid, and I feel that many of my own experiments, and 
many performed by others, have been vitiated for want of this 
knowledge. Take,Tor example, the effect of a vacuum, which 
was observed by Sir Charles Scudamore to promote coagula¬ 
tion. This has been considered by Dr. Richardson as an 
illustration of his theory, the vacuum being supposed to act 
by favoring the escape of ammonia. I have lately inquired 
into this subject, and I feel no doubt whatever that the 
greater rapidity of coagulation in a vacuum depends simply 
on the greater disturbance of the fluid. I made the following 
experiment:—I filled three bottles such as these from the 
throatjof a bullock, placed one of them under the small bell jar 
of an air-pump in good order, and exhausted it, leaving the 
other two undisturbed. The blood happened to be slow in 
coagulating; and at the end of about forty minutes, in the 
vessels where the blood had been undisturbed, there was only 
a slight film of coagulum on the surface, whereas the blood 
under the vacuum was found on examination to have a very 
thick crust of clot upon it. But during the process of ex¬ 
haustion the blood had bubbled very much. Indeed, anj^ 
exhaustion of blood recently drawn which is sufficient to 
cause the evolution of its gases induces great bubbling, so 
that the pump cannot be used freely for fear of the froth 
overflowing. To this disturbance, involving the exposure of 
successive portions of blood in the bubbles to the sides of the 
vessels, I was inclined to attribute the more rapid coagula¬ 
tion ; but in order to prove the point I stirred for a few 
seconds the blood in one of these vessels hitherto undisturbed. 
After eight minutes I emptied the three vessels. I found 
that the blood which had not been disturbed at all, either by 
the vacuum or by the rod, was still almost entirely fluid, only 
