124 ON THE COAGULATION OF THE BLOOD 
in the heart and principal trunks; whereas, on the contrary, the more super- 
ficial parts are liable to temporary causes of stagnation, and occasionally to 
what amounts to practical severance from vascular and nervous connexion 
with the rest of the body ; and it is, so to speak, of great importance that the 
blood should not coagulate so speedily in the vessels of a limb thus circum- 
stanced as it does in the heart after it has ceased to beat. Were it not for this 
provision, the surgeon would be unable to apply a tourniquet without fear of 
coagulation occurring in the vessels of the limb. As an illustration of the im- 
portance of a knowledge of these facts, I may mention a case that once occurred 
in my own practice. I was asked by a surgeon in a country district to amputate 
an arm which he despaired of. The brachial artery had been wounded, as well 
as veins and nerves, and at last, being foiled with the haemorrhage, he wound 
a long bandage round the limb at the seat of the wound as tightly as he possibly 
could. It had been in this condition with the bandage thus applied for forty- 
eight hours when I reached the patient, and the limb had all the appearance 
of being dead. It was perfectly cold, and any colour which it had was of a livid 
tint. But having been lately engaged in some of the experiments which I have 
been describing, and having thus become much impressed with the persistent 
vitality of the tissues and the concomitant fluidity of the blood, I determined 
to give the limb a chance by tying the brachial artery. Before I left the patient’s 
house he had already a pulse at the wrist, and I afterwards had the satisfaction 
of hearing that the arm had proved a useful one. 
One of the two arguments in favour of activity on the part of the vessels asa 
cause of the fluidity of the blood having been completely disposed of, let us now 
consider the other, viz. the rapid coagulation of blood shed into a basin, appearing 
at first sight to imply a spontaneous tendency of the blood to coagulate, such as 
would have to be counteracted by the vessels. This also has proved fallacious. 
In the first place it appears that the coagulation, after all, does not go on 
in a basin so suddenly as one would at first sight suppose, but always com- 
mences in contact with the foreign solid. When blood has been shed into 
a glass jar, if, on the first appearance of a film at the surface, you introduce 
a mounted needle curved at the end between the blood and the side of the glass 
and make a slight rotatory movement of the handle, you see through the glass 
the point of the needle detaching a layer of clot whatever part you may examine. 
The process of coagulation having thus commenced in contact with the surface 
of the vessel into which the blood is shed, may, under favourable circumstances, 
be ascertained to travel inwards, like advancing crystallization, towards the 
centre of the mass. It appears, however, that this extension of the coagulating 
* See above, p. 85. 
