e normal or
morbid. If the latter, the tissue becomes congested or inflamed.

CONGESTION.

Congestion is an unnatural accumulation of blood in a part. Excessive
accumulation of blood may be normal, as in blushing or in the red face
which temporarily follows a violent muscular effort, or, as in the
stomach or liver during digestion, or in the lungs after severe work,
from which, in the latter case, it is shortly relieved by a little rapid
breathing. The term congestion, however, usually indicates a morbid
condition, with more or less lasting effects. Congestion is active or
passive. The former is produced by an increased supply of blood to the
part, the latter by an obstacle preventing the escape of blood from the
tissue. In either case there is an increased supply of blood, and as a
result increased combustion and augmented nutrition.

ACTIVE CONGESTION.

Active congestion is caused by--

(1) _Functional activity._--Any organ which is constantly or excessively
used is habituated to hold an unusual quantity of blood; the vessels
become dilated; if overstrained the walls become weakened, lose their
elasticity, and any sudden additional quantity of blood engorges the
tissues so that they can not contract, and congestion results. Example:
The lungs of a race horse, after an unusual burst of speed or severe
work, in damp weather.

(2) _Irritants._--Heat and cold, chemical or mechanical. Any of these,
by threatening the vitality of a tissue, induce immediately an augmented
flow of blood to the part to furnish the means of repair--a hot iron,
frostbites, acids, or a blow.

(3) _Nerve influence._--This may produce congestion either by acting on
the part reflexly or as the result of some central nerve disturbance
affecting the branch which supplies a given organ.

(4) _Plethora and sanguinary temperament._--Full-blooded animals are
much more predisposed to congestive diseases than those of a lymphatic
character or those in an anemic condition. The circulation in them is
forced to all parts with much greater force and in large quantities. A
well-bred, full-blooded horse is much more subject to congestive
diseases than a common, coarse, or old, worn-out animal.

(5) _Fevers._--In fever the heart works more actively and forces the
current of blood more rapidly; the tissues are weakened, and it requires
but a slight local cause at any part to congest the structures already
overloaded with blood. Again, in certain feve