120 ON THE COAGULATION OF THE BLOOD 
part of the tube, the ammonia in the blood was so strong as to prevent coagula- 
tion altogether. 
This experiment illustrates how fitted the ammonia is to maintain the 
fluidity of blood, and also how apt it is, when present in the blood, to fly speedily 
off from it, leaving it unimpaired in its coagulating properties ; and it must be 
confessed that the end of the tube sealed with a small clot resembled most 
deceptively the extremity of a divided artery similarly closed. But although 
the experiment seems in so far to favour the ammonia theory, it will tell differ- 
ently when I mention the object with which it was performed. 
It appeared to me that, if the cause of the fluidity of the blood 
was free ammonia, then, if I provided an ammoniacal atmo- 
sphere in the tube, and introduced blood by pressure directly 
from the vein into this ammoniacal atmosphere, this blood, 
lying between the strong ammoniacal atmosphere on the 
one side and the ammonia naturally present in the blood 
within the vein on the other side, ought to remain fluid ; and 
if it did remain fluid, this would tend to confirm the ammonia 
theory by making it appear that the volatile material was the 
same at both ends of the tube. But, to my disappointment, I 
invariably found that if I drew away the tube after a few 
minutes only had elapsed, there was already a clot in its ex- 
tremity ; in other words, the ammonia had diffused from the 
end of the tube into the blood within the vein as into a non- 
ammoniacal atmosphere. This experiment alone, if duly 
considered, would, I think, suffice to show that the blood does 
not contain enough ammonia to account for its fluidity. 
One more experiment, however, may be adduced with 
5 the same object. I mounted a short but wide glass tube, open 
at both ends (T, Fig. 5), upon the end of a piece of strong wire, W, and con- 
nected with the latter a coil of fine silver wire, S, so that it hung freely in 
the tube. I then opened the carotid artery of a horse, and through the wound 
instantly thrust in the apparatus so far that I was sure the tube lay in the 
common carotid, which in veterinary language means the enormous trunk 
common to both sides of the neck of the animal. The tube being open at both 
ends, and slightly funnel-shaped at that end which was directed towards the 
heart, had thus a full current of arterial blood streaming through it. Having 
ascertained how long the arterial blood took to show the first appearance of 
coagulation in a watch-glass, I very soon after removed the apparatus, and, on 
taking out the coil of silver wire, found that it was already crusted over with 
Fic. 5; 
