ON, THE, COAGULATION OF THE BLOOD 23 
already commenced, as I can ascertain by squeezing the vessels between my 
fingers. But now that I lay open the vessel, you observe that the chief mass 
of its contained blood is still fluid, and we shall at all events have an opportunity 
of seeing that what is now fluid will in a short time be coagulated. It is an 
interesting circumstance with reference to the question which we are now con- 
sidering, that the coagulation always begins in contact with the vein, indicating 
that it is not the wall of the vessel that keeps the blood fluid, but that, on the 
contrary, the wall of the vessel, when deprived of vital properties, makes the 
blood coagulate. 
The observation of the persistent fluidity of the blood in these large vessels 
furnished the opportunity of making a very satisfactory experiment, which I 
hoped to have exhibited before the Society, but as there was some clot in the vein 
I did not think fit to run the risk of failure. The experiment is performed in the 
following way. A piece of steel wire is wound spirally round one of the veins 
in its turgid condition, and with a needle and thread the coats of the vessel 
are stitched here and there to the wire, care being taken to avoid puncturing 
the lining membrane, and thus the vessel is converted into a rigid cup. Two 
such cups being prepared, and the lining membrane of the vein being everted 
at the orifice of each so as to avoid contact of the blood with any injured tissue, 
I found that, after pouring blood to and fro through the air in a small stream 
from one venous receptacle into the other half a dozen times, and closing the 
orifice of the receptacle to prevent drying, the blood was still more or less com- 
pletely fluid after the lapse of eight or ten hours. On the other hand, if a fine 
sewing needle is pushed through the wall of an unopened vessel so that its end 
may lie in the blood, it is found on examination, after a certain time has elapsed 
that the needle is surrounded with an encrusting clot. It is scarcely necessary 
to point out how entirely the ammonia theory and the oxygen theory, as well 
as that of rest, fail to account for facts like these. 
While the blood may remain fluid for forty-eight hours in the jugular vein oi 
a horse or an ox, it coagulates soon after death in the heart of very small animals, 
such as mice, so that it 1s obvious that the continuance of fluidity in small 
vessels is not due to their small size. 
It is a very curious question, What is the cause of the blood remaining 
so much longer fluid in some vessels than in others? I believe that we must 
accept it simply as an ultimate fact, that just as the brain loses its vital pro- 
perties earlier than the ganglia of the heart, so the heart and principal vascular 
trunks lose theirs sooner than the smaller vessels of the viscera, or than more 
superficial vessels, be they large or small. We can see a final cause for this, 
so to speak. So long as the heart is acting, circulation will be sure to go on 
