132 ON THE COAGULATION OF THE BLOOD 
of the living vessels retaining it there. It might be that an action of the living 
vessels might chain down the ammonia and prevent it from escaping, whereas, 
when shed from the body, it would be free to escape. 
This notion was, I confess, at one time entertained by myself; and one 
of my earliest experiments was performed with a view to the corroboration 
of the ammonia theory as applied to blood outside the body. It seemed to 
me desirable that further evidence should be afforded of the effect of mere 
occlusion from air in maintaining the blood fluid. If the ammonia theory 
were true, then if blood could be shed directly from a living vessel into an air- 
tight receptacle composed of ordinary matter it ought to remain fluid. For 
this purpose, I made the following experiment :— 
I tied into the jugular vein, V (Fig. 1), of a sheep 
a long vulcanized india-rubber tube, T, adapted 
by means of short pieces of glass tube at its 
extremities, both ends being connected with the 
vessel so that the current of blood might be per- 
mitted to flow through the tube, and then con- 
tinue its natural course. When it had been 
ascertained that the blood was circulating freely 
through the tube, which could be readily done 
by placing the finger on the cardiac aspect of the 
vein, which was then made to swell if the circula- 
tion was proceeding through the tube, pieces of 
string well waxed were tied at intervals of about 
two inches round the tube, which was thus 
converted into a number of air-tight receptacles containing blood, which 
certainly had no opportunity for the escape of ammonia. The tube was then 
removed, and I found, in accordance with the view which I was then disposed 
to entertain, that the blood, instead of coagulating completely in a few minutes 
as it would have done if shed into a cup, remained partially fluid in these recep- 
tacles after the lapse of three hours. But I have since found that if the experi- 
ment be repeated in the same way as regards its earlier stages, and if, after 
a few of the strings have been tied on, the tube be cut across, the blood which 
is in the part of the tube in the vicinity of the air, just like that which is in the 
air-tight receptacles, remains fluid in part for two or three hours. In short, 
that my precautions in ensuring that these receptacles should be air-tight were, 
in so far as they applied to that object, utterly unnecessary. I mention this 
partly as an illustration of the deceptions to which one is liable in this inquiry, 
and partly because the experiment thus modified seems to tell as clearly against 
FIG. I. 
