198 ON THE COAGULATION OF THE BLOOD 
of fibrine, it resembled in its interior an artery or a vein.’ The force of the blood 
not being able to tell upon the clot and disturb it, the clot ceased to induce 
further coagulation, and became organized and invested with endothelium. 
We see the same thing illustrated in the different behaviour of the blood- 
clot above and below a ligature applied upon an artery in its continuity. When 
such a ligature was applied in the old-fashioned way, in the shape of a silk thread, 
used without any antiseptic precautions, with the ends left long, it had to come 
away by suppuration, and there was serious danger of secondary haemorrhage. 
But if this did occur, it was commonly not, as might have been expected, from 
the cardiac side, where the seat of ligature was subjected to the full force of the 
ventricular contractions, but from the distal side, where the pressure was com- 
paratively feeble. The lgature having been applied sufficiently tightly to 
rupture the internal and middle coats, there necessarily occurred as an imme- 
diate result a certain limited amount of coagulation upon the injured tissues. 
On the cardiac side, where the force of the blood driven by the heart against 
the obstruction told powerfully at every stroke, the clot was perpetually dis- 
turbed, and infallibly coagulation occurred up to the first considerable branch, 
producing a substantial resisting plug. But at the distal side, if the circumstances 
of the anastomosing circulation were such that there was no pulsation, there 
might be no extension whatever of the undisturbed primary coagulum, so that 
a mere trace of clot was found on pathological examination. 
I have hitherto dwelt on the view first advanced by myself and now, I believe, 
generally accepted—that the fluidity of the blood is not due to an active operation 
of the living vessels. But I am far from holding the opinion that there is no 
part of the vascular system that actively opposes coagulation. If transfusion is 
practised in the ordinary manner—say by filling a syringe with blood and 
injecting it into the veins of the patient—the blood is subjected to the influence of 
an ordinary solid, which would inevitably induce coagulation within the vessels, 
unless there were some counteracting agency at work. It is astonishing how 
very short a period of contact with an ordinary solid determines the mutual 
reaction of the corpuscles and the liquor sanguinis. Yet no coagulation 
occurs as the result of such an operation. It is, I presume, in the capillary 
system that the correcting influence is exerted. 
Again when intense inflammatory congestion is produced by the application 
of some irritant substance to the web of a frog’s foot, we see that the corpuscles, 
both red and white, adhere to one another and to the walls of the vessels, and 
block the capillaries. Mechanical violence is one of the many irritating agencies 
which produce such congestion ; and from what we know of the effects of the 
* Syme’s Principles of Surgery, 5th edition, p. 140. 
