COAGULATION OF THE BLOOD. 
695 
the phenomenon ; but the fact that lymph is afterwards 
exuded from this part of the vessel, shows that the case is 
really one of limited traumatic arteritis. 
But if the coagulation within inflamed vessels thus receives 
a solution from the results of the last-mentioned experiment, 
still more unequivocally, at least to most of my hearers, is 
the coagulation in gangrene explained, such as occurred, for 
instance, in the case which has been described. 
Again, it is well known that contused wounds bleed very 
little, the ends of the divided arteries becoming speedily 
plugged with a long coagulum. The only explanation which 
Sir Charles Bell could offer of this remarkable provision of 
nature was, that the living vessels had a special faculty of 
preventing the blood from exercising friction upon their 
lining membrane, but that the contused artery, having lost 
its vitality, the blood became arrested by friction, and coagu- 
lated. We now see that there was much more truth in this 
theory than has been generally supposed, though the loss of 
vitality in the vessel does not operate in the manner which 
Sir Charles imagined. 
It has been found difficult to understand why the fact of 
the arteries being converted into calcareous tubes should im- 
press upon the blood within them a tendency to coagulate in 
atheromatous degeneration of the vessels. The impairment, 
or entire loss of vitality connected with such a condition, will 
now be found a sufficient explanation. 
The coagulation in aneurism is now equally comprehensi- 
ble, the walls of the sac consisting either of degenerated or 
torn coats of the vessel, of inflamed surrounding tissues, or 
of layers of fibrine, each of these constituents being in a state 
of very low vitality. 
The rapid coagulation of lymph, which appears to be nei- 
ther more nor less than the fibrine of effused liquor sanguinis, 
contrasts, in a very striking manner, with the lengthened 
period during which blood extravasated into the cellular tissue 
may retain its fluidity. But the fact that the liquor sanguinis 
is exuded among tissues that are in a state of inflammation, 
and so impaired in their vital energies, renders the circum- 
stance in question easily intelligible. 
With regard to the nature of the influence exercised by 
the living vessels upon the blood within them, it might be 
conceived to be either of a positive or negative character. It 
might be imagined, either that the blood has a natural ten- 
dency within the vessels to comport itself as it does when 
outside the body, and that this tendency is counteracted by 
an active operation of the living tissues, or, that the vital 
