INS PRACTICAL ASPECTS 195 
present in the shrinking of the fibrine, which, as a matter of theory, seems quite 
as likely to have such an influence on the blood-corpuscles as the attractions of 
an ordinary solid. If such be the true state of the case, the clot must go on 
perpetuating itself indefinitely, however slowly.’ 
But how are we to explain the non-extension of the clot within the vessels 
in the cases referred to ? How are we to explain the fact that it did not spread 
from the vicinity of the tight cord in the sheep’s foot, and does not extend beyond 
the vicinity of the wound in the amputated limb? Again, why is it that the 
coagulum never propagates itself from the wound in the vein after phlebotomy ? 
That wound—intentionally made somewhat gaping—is certainly, in the first 
instance, occupied by blood-clot. The equable flow of the venous blood does 
not disturb it. It is an undisturbed coagulum. But it must often happen that 
the clot projects more or less into the calibre of the vessel, in which case the 
blood, at its lee side, will lie at rest in contact withit. Yet the indefinite extension 
of the coagulum, which the analogy of the blood in the glass tube would lead 
us to anticipate, never occurs; and we reckon with confidence on the wound 
in the vein simply healing without interference with its calibre. 
These remarkable differences between the behaviour of a coagulum in a glass 
tube and within the living vessels may, perhaps, have light thrown upon them 
by a fact which I have on a previous occasion brought before the attention of 
this Society. I first observed it, eighteen years ago, in an attempt that I made 
to obtain pure blood-serum from a horse; letting blood, with antiseptic pre- 
cautions, from the carotid artery into a flask that had been purified by heating 
it toa very high temperature. To my great astonishment, I found that, although 
the blood of the horse coagulated as usual in the flask, the clot did not shrink 
in the least. Though I kept it for many days, yet there was not a drop of 
serum to be seen upon its surface, and the sides of the clot remained in contact 
with the wall of the flask. This was made particularly striking by the circum- 
stance that masses of aggregated red corpuscles, resembling grains of sand, 
as before described, were to be seen touching the glass in the lower part of the 
buffy coat. This, I need hardly say, astonished me immensely ; and I imagine 
it was the first time that a blood-clot was ever seen not to shrink and press out 
serum. 
It seemed hardly likely that this result could be due to the destruction of 
micro-organisms in the flask, although the heat had been applied for that purpose. 
* A good example of the indefinite extension of a clot outside the body is mentioned by Freund 
(op. cit.).. He found that, while blood might be kept fluid for an indefinite period in a vessel completely 
coated with paraffin, if the coating was deficient at any point, coagulation took place there and spread 
throughout the mass. 
O02 
