118 OPHIDIANS. 
of a muddy liquor, carries down the corpuscles which exist 
in it as soon as it is coagulated by heat. If, instead of allow- 
ing the blood to rest, it is beaten with rods, the fibrin still 
coagulates, and forms whitish and elastic filaments, which 
adhere to the rods, the blood-globules not being included, 
because they are detached by the agitation of the fluid. De- 
fibrinated blood no longer coagulates. 
It is easy to demonstrate with the blood of frogs, the glob- 
ules of which are too large to pass through filtering-paper, 
that fibrin is really in solution in the serous liquid, and does 
not constitute any part of the globules, as was long supposed. 
It is sufficient to pour upon a filter, previously moistened, 
the blood of a frog, at the moment of its extraction, to show 
that a portion of the liquid passes through the filter before 
the commencement of coagulation ; and after collecting this 
portion in a watch-glass the microscope will exhibit in it, after 
a short time, a colorless clot, which may be made visible by 
collecting it on a needle. This experiment does not succeed 
in human blood, nor in that of other mammiferee, because the 
fluid is more viscid, and the globules are sufficiently small to 
pass through the paper. 
Serum is a yellow, slightly viscid fluid, of a density of 
1.027 to 1.029, with a slightly saline taste, and coagulates at 
about 168.8°, which is a property of the albumen element. 
Several saline substances prevent coagulation, for example, 
sulphates of soda, the chlorides of sodium and potassium, 
nitrate of potassa, borax, &e., and the proportion of these 
salts must be about one-sixth of the weight of the blood. 
Dilute mineral acids also prevent the coagulation of blood, 
but impart to it an oily consistency. A temperature of 86° 
to 104° Fahr. appears to be the most favorable for coagula- 
tion, while cold retards it considerably. 
