COAGULATION OF THE BLOOD. 647 
to the operation of spongy platinum in promoting the com¬ 
bination of oxygen and hydrogen. 
It may be asked, how comes it that when the blood of a 
horse is shed into a cup, the buffy layer coagulates as rapidly, 
or nearly so, as the lower parts rich in corpuscles? 
This is indeed a question well worthy of careful study. 
We know that the liquor sanguinis left by the subsidence of 
the red corpuscles within a healthy vein is incapable of 
coagulating when shed, except in a slow manner, which is 
accounted for by the corpuscles that remain behind in it. 
Hence it appears that when the blood a3 a whole is shed into 
a glass, the agency of the ordinary solid leads the corpuscles 
to communicate to the liquor sanguinis, before they subside, 
a material, or at least an influence, which confers upon it a 
disposition to coagulate, though it still remains fluid for some 
time after they have left it. Just as we have seen that a very 
short time of action of the ordinary solid upon the blood, as 
a whole, is sufficient to give rise to coagulation, so we now 
see that, provided an ordinary solid be in operation, the 
presence of the corpuscles for but a little while is enough to 
make the liquor sanguinis spontaneously coagulable, though 
not immediately solidified. We shall see before concluding 
an illustration of the importance of this fact to pathology. 
It remains to be added, that serous membranes resemble 
the lining membrane 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, coagu¬ 
lated when let out. The same thing is well illustrated in a 
frog prepared like this 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 ventricle of the heart with forceps, and 
removed it with scissors. In a short time the whole of the 
animars 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 re¬ 
mained 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 a piece of clean glass placed in the 
blood in the peritoneum became speedily coated with co- 
agulum. Here it will be observed, not merely the liquor 
