128 ON THE COAGULATION OF THE BLOOD 
was now quickly inverted, and the vein was drawn off from over the mouth of 
the tube, which was then covered with gutta-percha tissue to prevent evapora- 
tion. After the inverted tube had been kept undisturbed in the vertical position 
for nineteen hours and three-quarters coagulable blood was obtained from the 
interior of the clot. 
We have seen that a clot has but very slight tendency to induce coagulation 
in its vicinity unless the blood has been acted on by an ordinary solid, and 
it is probable that with perfectly healthy blood it would be unable to produce 
such an effect at all. This appears to me to be very interesting physiologically, 
but especially so with reference to pathology. I must not go now fully into 
the circumstances that lead me to it, but I may express the opinion I have 
formed, that clot must be regarded as living tissue in its relation to the blood. 
It is no doubt a very peculiar form of tissue, in this respect—that it is soft, easily 
lacerable, and easily impaired in its vital properties. If disturbed, as in an 
aneurysm, it will readily be brought into that condition which leads to the 
deposition of more clot ; but if undisturbed, it not only fails to induce further 
coagulation, but seems to undergo spontaneous organization. I have seen 
a clot in the right side of the heart, and extending into the pulmonary artery 
and its branches, unconnected with the lining membrane of auricle or ventricle 
or with the pulmonary artery except at one small spot where it had a slight 
adhesion, developed into perfect fibrous tissue by virtue, it would appear, of its 
own inherent properties. Another observation which I once made, and which 
then completely puzzled me, now seems capable of explanation. In laying open 
the blood-vessels of a dead body I observed in many of the veins a delicate 
white lace-like tissue which evidently must have been formed from a clot. This 
I now believe to have had the same relation to the coagulum as the flimsy cellular 
tissue of old adhesions has to lymph. 
It may not be altogether superfluous to mention some other facts illustrative 
of the active influence of ordinary matter in promoting coagulation, and the 
negative character of the lining membrane of the vessels. I find that a needle 
introduced into one of the veins of the foot of a sheep for a much shorter time 
than is necessary to produce the first appearance of the actual deposit of fibrine 
upon it, leads after a while to coagulation where the needle had lain; in other 
words, that a foreign solid, by a short period of action on the blood, brings 
about a change that results in coagulation, though the blood still lies in the 
living vessels. I have also ascertained that after blood has been made to coagu- 
late in a particular vessel by introducing a needle into it, if the coagulum as 
well as needle is removed, and more fluid blood is allowed to pass in, this blood 
remains fluid for an indefinite period, showing that the needle had not impaired 
