30 DISEASES OF THE HORSE. 



CONGESTION. 



Congestion is an unnatural accumulation of blood in a^part. Ex- 

 cessive accumulation of blood may be nomial, 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- 

 sivel}^ 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 Aoav 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 refiexly 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 an}'' pa^t 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 tlie vessels and induces a 

 local predisposition to congestion. 



