If you cut your finger, or cut or break the skin on any part of your
body, you begin to bleed, for the simple reason that some of the tiny
blood vessels near the surface have been injured, and blood oozes from
them. But, after a few moments, the bleeding tends to stop, and, if the
cut is not a very severe one, it usually ceases of its own accord very
shortly. A sort of protecting crust is formed, and the flow of blood is
stopped by Nature’s own methods.
What has happened to cause the flow to cease? Various things, the most
important of which is “coagulation,” or clotting of the blood, as soon
as it is exposed to the air. It is very interesting to see just what
happens here--during this process of clotting.
The cause of clot-formation has been found to be the precipitation
of a solid form, the liquid plasma of the blood. This solid is in
the form of very minute threads, and hence is termed _fibrin_. The
threads traverse the mass of blood in every direction, interlacing, and
thus confining in their meshes all the solid elements of the blood.
They soon begin to contract, when out of the body, and form a minute
mesh-work or net, carrying within it the corpuscles of the blood. These
corpuscles within the fibrin form the _clot_.
After a time, a yellowish fluid forms on the outside of the clot;
this is the _serum_, and is squeezed out of the solid constituents
of the blood, as the latter dries like water from a squeezed sponge.
Altogether, about a third as much serum is formed on the clot as the
solid material of the clot itself!
Recent experiments conducted in Harvard University have shown that
the adrenal glands (one of the ductless glands in the body) will
hasten coagulation, and any strong emotion will do the same thing.
As most injuries are received during some strong emotion, this is
evidently another of Nature’s plans to hasten clotting and prevent the
unnecessary loss of blood.