ON THE COAGULATION OF THE BLOOD 113 
the ammonia theory as the original one seemed to tell in favour of it. Those 
receptacles which had been formed by the application of ligatures before the 
tube was opened afforded certainly no opportunity for the escape of ammonia, 
and yet in them the blood coagulated as quickly as in those which had com- 
munication with the air—implying that facility for the evolution of ammonia 
does not in itself affect the process of coagulation at all. 
How then, it may be said, is the persistent fluidity of the blood under 
these circumstances to be explained? That will become more obvious than 
I can make it at present in the sequel, but in the 
meantime I may observe that there are probably ez 
two explanations: one is, the coolness of the tube, 
and the other, far more important, that the blood, 
in slipping through this cylindrical tube, had had 
little opportunity of being influenced by its walls. 
The portion of the blood that came first in contact 
with the walls of the tube had coagulated ; and it 
is to be observed that I never found, in these ex- 
periments, the blood altogether fluid, even after a 
comparatively short time: there has always been 
a certain amount of coagulation, and only a certain 
amount of fluidity. A layer of blood having thus 
coagulated upon the internal surface of the tube, 
the fresh blood, which continued to flow through it, 
was not brought into contact with the walls of the 
tube at all, but with their lining of coagulated 
blood. 
It has been long known that if blood is stirred 
with a rod, the process of coagulation is promoted. 
It seemed desirable to ascertain distinctly whether 
the cause of this was the contact of the foreign 
solid, or the opportunity given for the escape of ammonia ; for it is quite true 
that, in the ordinary process of stirring blood, more or less air is mixed with it. 
For the purpose of determining this I devised a somewhat complicated experi- 
ment, which, however, it may be worth while to mention. I madean apparatus 
(Fig. 2) of two portions of glass tube, A and B, connected in a vertical position 
by means of vulcanized india-rubber, I, the lower portion of the glass tube being 
also connected by india-rubber, I’, with a wooden handle, which handle, H, was 
provided with an upright piece of wire, from which spokes projected in different 
directions, so that they would, when moved, act asa churn on any blood contained 
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