rpuscle is merely the
nucleus of a colorless corpuscle enlarged, flattened, colored and
liberated by the bursting of the wall of its cell. When blood is taken
from an artery and allowed to remain at rest, it separates into two
parts: a solid mass, called the clot, largely composed of fibrin; and a
fluid known as the _serum_, in which the clot is suspended. This process
is termed _coagulation_. The serum, mostly composed of _albumen_, is a
transparent, straw-colored fluid, having the odor and taste of blood.
The whole quantity of blood in the body is estimated on an average to be
about one-ninth of its entire weight. The distinctions between the
arterial and the venous blood are marked, since in the arterial system
the blood is uniformly bright red, and in the venous of a very dark red
color The blood-corpuscles contain both oxygen and carbonic acid in
solution. When carbonic acid predominates, the blood is dark red; when
oxygen, scarlet. In the lungs, the corpuscles give up carbonic acid, and
absorb a fresh supply of oxygen, while in the general circulation the
oxygen disappears in the process of tissue transformation, and is
replaced, in the venous blood, by carbonic acid. The nutritive portions
of food are converted into a homogeneous fluid, which pervades every
part of the body, is the basis of every tissue, and which is termed the
_blood_. This varies in color and composition in different animals. In
the polyp the nutritive fluid is known as _chyme_, in many mollusks, as
well as articulates, it is called _chyle_, but in vertebrates, it is
more highly organized and is called blood. In all the higher animal
types it is of a red color, although redness is not one of its essential
qualities. Some tribes of animals possess true blood, which is not red;
thus the blood of the insect is colorless and transparent; that of the
reptile yellowish; in the fish the principle part is without color, but
the blood of the bird is deep red. The blood of the mammalia is of a
bright scarlet hue. The temperature of the blood varies in different
species, as well as in animals of the same species under different
physiological conditions; for this reason, some animals are called
_cold-blooded._ Disease also modifies the temperature of the blood; thus
in fevers it is generally increased, but in cholera greatly diminished.
THE blood has been aptly termed the "vital fluid," since there is a
constant flow from the heart to the tissues and organs