608 
REMARKS ON COMPOSITION OF THE BLOOD. 
colour, resembling in this respect the blood of the inverte¬ 
brate class of animals. 
It can be readily imagined that a fluid, which nature em¬ 
ploys for such multitudinous purposes in the animal economy, 
is likely to be very complex in its elements, and such, indeed, 
is the case. To analyze these, even imperfectly, it is neces¬ 
sary, as a general rule, that the blood be first removed from 
its vessels. On this being done, it will be found that shortly 
afterwards a remarkable change takes place in it, and that it 
is now no longer fluid, but has assumed a solid form. This 
phenomenon is among the most interesting which belong to 
the blood, and clearly indicates that the fluid possesses an 
inherent capability of assimilating organic structure. From 
the time of Hunter down to the present period, the correct 
explanation of the phenomenon of coagulation—clotting— 
has occupied the attention of our ablest chemists and physio¬ 
logists; and perhaps it is not too much to say that, notwith¬ 
standing all the light which has been shed upon it, some 
darkness still enshrouds the solution of the problem. 
The time which elapses before the blood becomes solid 
will vary considerably, depending on many adventitious cir¬ 
cumstances. The coagulation is usually effected in ten or 
fifteen minutes, but in some instances many hours and even 
days will pass before it is completed. Before, however, 
alluding more particularly to either the clotting of the blood 
or the variations in the time required for its accomplish¬ 
ment, it will be necessary to describe the principal compo¬ 
nent parts of the fluid. 
On setting aside the coagulated mass and keeping it at 
rest for a short period, a transparent fluid is found to exude 
from it, which can easily be decanted off. This is the 
serum, or so-called watery part of the blood. 
The Serum. — Under all ordinary circumstances this con¬ 
stituent of the blood remains in a fluid condition, while the 
quantity which is exuded will be in proportion to the time 
the coagulum remains at rest, until the expiration of about 
thirty hours ; after which, however, but little more will be 
expelled naturally, although a still greater amount can be 
obtained by drying the clot. It is, therefore, evident that 
by the act of coagulation the serum is mechanically enclosed 
in the solidified mass, and that subsequently, by this under¬ 
going a certain degree of condensation, the greater part of 
it is squeezed out as water is expelled from a sponge by the 
application of pressure. 
Thus obtained, the serum is found to be a viscid fluid of 
a vellowish colour and having an alkaline reaction. Its 
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