96 PATHOLOGY. 



lu hemiplegia, a disease rarely witnessed in tlie horse, but to 

 which horned cattle are liable, congestion of the vessels of the 

 paralysed side is a prominent symptom. 



Atony of the arterial walls may be due to degeneration of 

 their muscular and internal coats. It is most commonly the 

 cause of the various congestions seen in old animals. 



Mechanical congestion occurs chiefly in the veins, and is pro- 

 duced by anything which interferes with the flow of the blood 

 through them, such as obstruction of the vein leading from a 

 part, arising from pressure upon its walls, or the pressure of a 

 thrombus or clot within its canal. Thus congestion may be in- 

 duced by the pressure of a tight bandage ; and again, congestion 

 of the portal vein is caused by cirrhosis or other disease of the 

 liver, which causes pressure upon its venous branches. Disease 

 of the valves of the heart produces fulness of both the pulmonary 

 and systemic veins. When the incompetency is limited to 

 the mitral valve, the congestion is mostly limited to the lungs, 

 while insufiiciency of the tricuspid causes congestion of the 

 systemic veins. The character of congestion beginning in the 

 veins is that the veins as well as the capillaries are distended, 

 giving the part an arborescent appearance, which has a much 

 more permanent character than congestion beginning at the 

 arteries. Arterial congestion, especially that of an active type, 

 very often disappears shortly after death by the 2^ost mortem 

 contraction of the vessels. 



In addition to mechanical obstruction to tlie flow of blood, 

 there are various and important causes of venous congestions, 

 such as diminished cardiac power, gravitation, an altered con- 

 dition of the blood, and defective secretions. 



1. Diminished cardiac 'power. — The contractile power of the 

 heart becomes diminished in many diseases, and death may 

 result, not so much from the original disease from which the 

 animal has been suffering, as from congestion of some vital 

 organ, more especially the lungs or the brain, arising from the 

 inability of the heart to propel the blood through the vessels of 

 such organ. The example most familiar to the veterinarian of 

 this form of congestion is acute congestion of the lungs caused by 

 over-exertion. Many instances of this occur in the hunting-field 

 during severe runs ; horses out of condition, and imfit for very 

 prolonged and severe galloping, falling down and rapidly sinking 



