30 DISEASES OF THE HORSE. 
CONGESTION. 
Congestion is an unnatural accumulation of blood in a part. Ex- 
cessive 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 indi- 
cates 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 sup- 
ply 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 exces- 
sively used is habituated to hold an unusual quantity of blood; 
the vessels become dilated; if overstrained the walls become weak- 
ened, lose their elasticity, and any sudden additional quantity of 
blood engorges the tissues so that they can not contract, and conges- 
tion 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 act- 
ing on the part reflexly or as the result of some central nerve dis- 
turbance 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 circula- 
tion in them is forced to all parts with much greater force and in 
large quantities. A well-bred, full-blooded horse is much more sub- 
ject 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 fevers, we find 
alteration of the blood itself, rendering it less or more fluid, which 
interferes with its free passage through the vessels and induces a 
local predisposition to congestion. 
