480 BUREAU OF ANIMAL INDUSTRY. 



tional 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 perfeotl34iealthy tissues 

 are. Thus a horse which 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 librous tissues 

 which surround the vessels. Where the changes produced bj^ 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 

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

 the part is frequently painful to the animal from pressure of the eltu- 

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

 The secretion or excretion of glands maybe augmented or dhninished. 

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

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



PASSIVE CONGESTION. 



Passive congestion is caused by interference with the return of the 

 current of blood from a part. 



Old age and debility weaken the tissues and the force of the circu- 

 lation, 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 with effusions of the liquid parts of the 

 blood into the lymph spaces of the posterior extremities imd organs 

 of the pelvic cavity. 



Tumors or other mechanical obstructions, b}^ pressing on the Acins, 

 retard the flow of blood and cause it to back up in distal parts of the 

 body, causing passive congestion. 



The alterations of passive congestion, as in active congestion, consist 

 of an increased quantity of blood in the vessels and an exudation of its 

 fluid into the tissues surrounding them, but in passive congestion we 

 have a dark thick l)lood which has lost its oxygen, instead of the rich 

 combustible blood rich in oxygen which is found in active congestion. 



The ternaination of congestion is b}' resolution or inflammation. In 

 the first case, the choked-up blood vessels find an outlet for the exces- 

 sive amount of blood and are relieved; the transuded serum or fluid of 

 the blood is reabsorbed, and the part returns almost to its normal con- 

 dition, with, however, a tendency to weakness predisposing to future 

 trouble of the same kind. In the other case further alterations take 

 place, and we have inflammation. 



