479 



(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 

 alreadj^ 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. 



(G) Warm climate and summer heat. — Warmth of the atmosphere 

 relaxes the tissues; it demands of the animals less blood to keep up 

 their own body temperature, and the extra quantity accumulates in 

 the blood-vessel system. It causes sluggishness in the performance of 

 the organic functions, and in this way it induces congestion, especially 

 of tlie internal organs. So we find founders, congestive colics, and 

 staggers more frequent in summer than in winter. 



(7) Previous congestion. — Whether the previous congestion of any 

 organ has been a continuous normal one, that is, a repeated functional 

 activity, or has been a morbid temporary overloading, it always leaves 

 the walls of the vessels weakened and more predisposed to recurrent 

 attacks from accidental causes than i)erfectly healthy tissues are. 

 Thus a horse Avhich has had a congestion of the lungs from a severe 

 drive is apt to have another attack from even a lesser cause. 



The alterations of congestion are distention of the blood vessels, 

 accumulation of the cellular elements of the blood in them, and effu- 

 sion of a portion of the liquid of the blood into the fibrous tissues 

 which surround the vessels. Where the changes produced by conges- 

 tion are visible, as in the eye, the nostril, the mouth, the genital 

 organs, and on the surface of the body in white or unpigmented ani- 

 mals, the part appears red from the increase of blood; it becomes 

 swollen from the effusion of liquid into the sponge-like connective tis- 

 sues; it is at times more or less hot from the increased combustion; the 

 part is frequently painful to the animal from pressure of the effusion 

 on the nerves, and the function of the tissue is interfered with. The 

 secretion or excretion of glands may be augmented or diminished. 

 Muscles may be affected with spasms or may be unable to contract. 

 The eyes and ears may be affected Avith imaginary sights and sounds. 



PASSIVE COXGESTION. 



Passive congestion is caused by interference with the return of the 

 current of blood from a part. 



Old age and del) Hit y weaken the tissues and the force of the circula- 

 tion, especially in the veins, and retard the movement of the blood. 

 We then see horses of this class with stocked legs, swelling of the 

 sheath of the penis or of the milk glands, and of the under surface of 

 the belly. We find them also Avith effusions of the liquid parts of the 

 blood into the lymph spaces of the posterior extremities and organs of 

 the pelvic cavity. 



