IIO ON THE COAGULATION OF THE BLOOD 
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 fibrine, which, in its turn, may be 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 fibrine ? 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 the blood is removed from the body. 
With regard to the first point, the essential nature of the process of coagula- 
tion, different views have been entertained. John Hunter was of opinion that 
the coagulation of the blood, the solidification of the fibrine, 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 retains the faculty of coagulating when water is added to the 
mixture. Mr. Gulliver, on one occasion, kept blood fluid, by means of nitre, 
for upwards of a year, but found that it still coagulated on the addition of water. 
It seems exceedingly improbable that any part of the human body should retain 
its vital properties after being thus pickled for more than a year. But 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 particular 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 ourselves 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 pathologist. When, therefore, I use the term ‘ vital pro- 
perties ’, I mean simply properties peculiar to the tissues as components of the 
healthy living body. 
Turning now to the other aspect of the subject of coagulation—the cause 
of the occurrence of that process on the escape of the blood from the living 
body—we find that here again various theories have been held, which may 
be divided into mechanical, chemical, and vital. The mechanical theory was, 
that mere rest of the blood was sufficient to cause coagulation. I say this was 
the theory ; but I believe it will be found to be still taught by many that the 
cause of the coagulation of the blood in an artery which has been tied is its 
stagnation in the vicinity of the ligature. 
As to the chemical theories they have been various. One very natural 
