681. 
COAGULATION OF THE liLOOD. 
form a complicated network among the blood-corpuscles, and 
from their tenacity are the cause of the firmness of the clot. 
Soon after the process of solidification or coagulation is com¬ 
plete, the fibrin exhibits a disposition to shrink, and squeezes 
out from among the corpuscles entangled in its meshes a 
straw-coloured fluid termed the serum, very rich in albumen 
•—in fact, very similar in chemical composition to the fibrin, 
which, in its turn, maybe said to be identical chemically with 
the material of muscular fibre. 
The question before us, therefore, is, What is the cause of 
the development of this solid material—the fibrin ? The 
subject may be looked at in two aspects: first, as to the 
essential nature of the process of coagulation ; and, secondly, 
as to the cause of its occurrence when tlie blood is removed 
from the bodv. 
•/ 
AYith regard to the first point, the essential nature of the 
process of coagulation, different views have been entertained. 
John Hunter was of opinion that the coagulation of the blood 
■—the solidification of the fibrin, was an act of life—analogous, 
in some respects, to the contraction of muscular fibre. This, 
on the other hand, was made,very unlikely by the observation 
of his contemporary, Mr. Hewson, that blood may be kept in 
the fluid state by the addition of various neutral salts, but re¬ 
tains the faculty of coagulating when water is added to the 
mixture. IMr. Gulliver, on one occasion, kept blood fluid, by 
means of nitre, for upwards of a year, but found that it still 
coagidated on the addition of water. It seems exceedingly 
improbable that any part of the human body should retain its 
vital properties alter being thus pickled for more than a year, 
lint here I would wish to make an explanation of the use of 
this term vital properties.” When employing it I do not 
wish to commit myself to any jiarticular theory of the nature 
of life, or even to the belief that the actions of living bodies 
are not all conducted in obedience to physical and chemical 
laws. But it appears that every component tissue of the 
human body has its own life, its own health, just as we our¬ 
selves have ; and as the actions of living men will ever retain 
their interest, whatever views be entertained of the nature of 
life, so must the actions of the living tissues ever continue to 
be essential objects of study to the physiologist and patho¬ 
logist. When, therefore, I use the term ‘‘vital properties,” 
I mean simply properties peculiar to the tissues as com¬ 
ponents of the healthy living body. 
Turning now to the other aspect of the subject of coagu¬ 
lation—the cause of the occurrence of that process on the 
escape of the blood from the living body—we find that here 
