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674 . GENERAL PATHOLOGY. —
lively little importance. The energies of the body, and especially its
nutritive powers, upon which these energies depend, are closely con-
nected with the corpuscular elements of the blood, especially the red
corpuscles. Their importance is shown by the fact that animals bled
nearly to death may be resuscitated by the injection of these corpuscles
in serum. From what is known of their physiological relations, it
might be inferred that the eifect of an excessive quantity of blood with
the full proportion of red corpuscles, or of a superabundance of the red
corpuscles without an excess of fluid, would produce over-activity of the
circulation and a disposition to undue excitation of the organs of the
body. Such effects, in fact, constitute the phenomena of the condition of
plethora. The power of the heart's action is increased ; sensibility and
muscular irritability are augmented ; some rise in the temperature may
be noted ; the brain is more prone to excitement ; and the whole body
takes on a full and rotund outline. Pain in the head is liable to be
produced by excitement or by stimulants, on account of the unusual
power of the circulation ; and this condition is thought to involve a
liability to cerebral congestion. Febrile attacks are rendered more
intense, and acute inflammations are more readily excited. It is
important to discriminate between plethora and other morbid con-
ditions. In pregnancy the fluid elements of the blood are often nuich
increased without a true plethora. In this case there is not an abnor-
mal increase of the red blood-globules, and other signs of the state of
plethora are wanting. Abnormal fulness of the blood-vessels from
some impediment to the returning veins might sometimes be mistaken
for this condition.
A tendency to plethora may be inherited, or it may be acquired by
over-feeding on rich foods, wines, etc., connected with diminished
expenditure of blood-constituents in the nutrition of the body. This
is directly favored by sedentary habits, the digestive and assimilative
functions remaining active.
Experiments in the transfusion of blood in animals give us some idea
of the extent to which the volume of the blood maybe increased. AVorm
Mueller injected the defibrinated blood of dogs into other dogs, and by
careful experiment found that the normal amount of blood might be
increased one-half or three-fourths without materially endangering the
health of the animal, and double the normal quantity would be borne
without much apparent inconvenience. If, however, the quantity was
increased much beyond this, perturbations of the circulation occurred,
and the animal died within a day or two. It appears from these
experiments that the excess of blood injected is quickly disposed of
that within three or four days there is only an excess of the globules,
and at the end of two weeks these also have disappeared. From the
results of these experiments it may be concluded that there is some
mechanism in the body having the power of regulating the amount
of the l^lood, but as to what this mechanism may be there is as yet
no definite knowledge.
Local Hyper/E.mia, or Congestion.—Local hyperfemia consists in
the presence of an undue amount of blood in a particular part. Tavo vari-
eties, differing in mode of origin and in character, are recognized : these are