Peis PRACTICAL ASPECTS 193 
by the butcher. The blood remains fluid for days in the veins of such feet, 
while, at the same time, the persistent vitality of the vessels is shown by the fact 
that they contract when exposed by reflexion of the skin.1 Now it happened 
that the butcher, in order to keep the sheep from struggling, always tied the 
feet together with a firm cord applied below the part where my bandage for 
retaining the blood was passed round ; and I invariably found the blood coagu- 
lated in the superficial veins at the part where they had been pinched between the 
cord and the bone. There is no reason to suppose that the temporary application 
of the cord had deprived the veins of their vitality at the part subjected to its 
pressure. If the sheep had been released, I have no doubt whatever that the 
veins would have remained alive. But though the vessels had not been wounded 
but only squeezed, only had their vital energies temporarily impaired, never- 
theless the blood had coagulated in them at the part so treated. Just as by 
pinching a portion of the web of a frog’s foot with the padded ends of a pair of 
dressing forceps you can induce, by the irritation of mechanical violence, an 
intense degree of inflammatory congestion, in which the pigment cells for the 
time being have their vital functions of diffusion and concentration of the pig- 
ment perfectly suspended, and yet are in a condition which is recoverable,” so 
did these veins, subjected to a similar agency, experience, though unwounded, 
a temporary prostration of their vital power. Thus it appears that the living 
tissues, which, while in a healthy active state, differ from ordinary solids in not 
occasioning the coagulation of the blood, themselves act like ordinary solids, and 
induce coagulation when their vital energies are suspended. 
Another point to which my investigations were at that time directed was 
the behaviour of the blood-clot in relation to coagulation. I came to the conclu- 
sion that, in a healthy state of the blood, an undisturbed coagulum resembles 
living tissue in its behaviour with regard to coagulation ; that an undisturbed 
clot does not induce coagulation in its vicinity is a most important truth if it 
be such. This is well illustrated by the fact with regard to the sheep’s foot, 
to which I have already referred. We have seen that, on the one hand, where 
the tight cord had pressed the veins, coagulation occurred in those veins, but 
on the other hand that the blood remained permanently fluid in other parts of 
the same vessels. In other words, the clot induced by the action of the cord 
upon the veins had not been able to spread, although the blood in the veins 
was perfectly at rest; the clot could not propagate itself. The same thing is 
* The blood in the amputated limb becomes gradually impaired in its coagulating property. A few 
hours after amputation it is found to clot more slowly than at first when exposed to the influence of 
ordinary solids, and after some days fails to coagulate at all. 
* See a paper by the author ‘On the Early Stages of Inflammation’, Phil. Tvans. Part I, for 1858, 
p. 682 (page 209 of this volume). 
LISTER I O 
