132 ON THE COAGULATION OF THE BLOOD 
It remains to be added that serous membranes resemble the hning mem- 
brane of the blood-vessels in their relations to the blood, as is implied by John 
Hunter’s observation that blood which had lain for several days in a hydrocele 
coagulated when let out. The same thing is well illustrated in a frog prepared 
like this which I now exhibit. About four hours ago, a knife having been passed 
between the brain and cord to deprive the creature of voluntary motion in the 
limbs and trunk, the peritoneal cavity was laid open in the middle line, and its 
edges being kept raised and drawn aside by pins, I seized the apex of the ven- 
tricle of the heart with forceps and removed it with scissors. In a short time 
the whole of the animal’s blood was in the peritoneum, and it may be seen that 
it is still fluid in spite of this long-continued exposure. When I first performed 
the experiment three years and a half ago, the weather being cool (about 45° 
Fahr.) and a piece of damp lint being kept suspended above the frog to prevent 
evaporation and access of dust, I found that the blood remained fluid in the 
peritoneal cavity for four days, except a thin film on the surface and a crust of 
clot on the wounded part of the heart ; but apiece of clean glass placed in the 
blood in the peritoneum became speedily coated with coagulum. Here, it will 
be observed, not merely the liquor sanguinis, but the corpuscles also were present 
in the serous cavity, yet no coagulation took place in contact with its walls. 
I think it probable, though not yet proved, that all living tissues have 
these properties with reference to the blood. We know that the interstices 
of the cellular tissue contain coagulable fluid, and I have seen anasarcous liquid 
coagulate after emission, but this indeed may possibly have been merely liquor 
sanguinis coagulating in consequence of slight admixture of blood-corpuscles 
from the wounds made in obtaining it. 
Looking now at the principal results which we have arrived at, it must, 
in the first place, be admitted that the ammonia theory is to be discarded as 
entirely fallacious. The fact that this theory is exceedingly plausible, and has 
been supported by many ingenious arguments and experiments, is of course 
no reason why we should retain it if unsound. On the contrary, the more 
specious it is the more necessary is it that it should be effectually cleared away, 
for it mystifies the subject of coagulation most seriously ; and I may say, for 
my own part, that it has cost me an amount of experimental labour of which 
the illustrations brought forward this evening convey but little idea. Still 
these have been, I trust, sufficient to show that the coagulation of the blood is 
in no degree connected with the evolution of ammonia, any more than with 
the influence of oxygen or of rest. The real cause of the coagulation of the 
blood, when shed from the body, is the influence exerted upon it by ordinary 
matter, the contact of which for a very brief period effects a change in the blood, 
