ON EEE COAGULATION, OF THE BLOOD 120 
coagulum. Yet here assuredly there had been no opportunity for the escape 
of ammonia. 
From this experiment it is obvious that there is a very great difference 
between ordinary solid matter and the living vessels in their relation to the 
blood. But the same conclusion may be drawn much more simply from experi- 
ments which I had the opportunity of performing after making an observation 
which it seems strange should have been left for me to make, and which, I may 
say, was made by myself purely accidentally ; and this is, that the blood of 
mammalia, although it coagulates soon after death in the heart and the principal 
arterial and venous trunks, remains fluid for an indefinite period in the small 
vessels. If, therefore, a ligature be tied round the foot of a living sheep a little 
below the joint which is divided by the butcher, the foot being removed and 
taken home with the blood retained in the veins by the ligature, we have a ready 
opportunity of investigating the subject of coagulation, and of making observa- 
tions as satisfactory as they are simple. Here are two feet provided in the way 
I have alluded to. A superficial vein in each foot has been exposed. The 
veins I see have contracted very much since I reflected the skin from them 
before our meeting ; and I may remark that such contraction, dependent on 
muscular action, may occur days after amputation, indicating the persistence 
of vital properties in the veins. Now as I cut across this vein, blood flows out, 
fluid but coagulable. Into the vein of this other foot has been introduced 
a piece of fine silver wire, and when I slit up the vein you will see the effect 
it has produced. Exactly as far as the silver wire extends, so far is there a clot 
in this vessel. Now this experiment, very simple as it is, is of itself sufficient 
to prove the vital theory in the sense that the living vessels differ entirely from 
ordinary solids in their relation to the blood. It is perfectly clear that by 
introducing a clean piece of silver wire (and platinum or glass or any other 
substance chemically inert would have had the same effect) I do not add any 
chemical material or facilitate the escape of any, and yet coagulation occurs 
round about the foreign solid. 
Again, if a blood-vessel be injured at any part, coagulation will occur at 
the seat of injury. As a good illustration of this, and also as bearing upon the 
ammonia theory, I may mention the following experiment. Having squeezed 
the blood out of a limited portion of one of the veins of a sheep’s foot, and pre- 
vented its return by appropriate means, I treated the empty portion with caustic 
ammonia, the neighbouring parts of the vein being protected from the tritating 
vapour by lint steeped in olive oil. After the smell of ammonia had passed off, 
I let the blood flow back again and left it undisturbed for a while, when I found 
on examination a cylindrical clot in the part that had been treated with ammonia, 
