36 Veterinary Medicine. 



blood from the right heart ; disease of the right heart allowing a 

 reflux of blood into the veins ; or pressure by tumors or other- 

 wise on the great or small venous trunks. If in the heart or 

 lungs the whole systemic venous system becomes the seat of pas- 

 sive congestion ; if in a single venous trunk then only the parts 

 the venous radicles of which are tributary to this. We find ex- 

 amples of this in phlebitis, in compression by the swellings of 

 strangles, in the result of a bandage or ligature tied round a limb 

 at some distance from its extremity, and in the compression of 

 the iliac veins by a gravid womb. 



2d. Diminished force of the blood current in the veins, as from 

 old age or great debility and especially from weakness of the 

 heart's action. Also from disease of the arterial coats which im- 

 pairs their tonicity. The force being too weak to force the blood 

 actively through the capillaries and veins, it becomes unduly 

 charged with carbon dioxide and other products of tissue waste, 

 so that nutrition suffers and the walls of the capillaries lose their 

 vital force. This condition is aggravated in the hind limbs by 

 the distance from the heart, and the dependent position, and in 

 decubitus by the compression of the vessels of the limbs. Also 

 by injuries to the vaso-motor nerve supply as oedema appeared 

 in the hind limb after tying of the femoral vein in animals the 

 abdominal sympathetic of which had been cut, but not in animals 

 in which this nerve was left in its normal condition (Ranvier) . 



3d. Gravitation in weak states of the circulation must be looked 

 upon as a cause of venous congestion. This is seen in the ex- 

 amples of hypostatic congestion and oedema seen in the lungs and 

 other internal organs in low conditions and in the advanced stages 

 of debilitating diseases, and in certain cases of stocking of the 

 limbs in horses. 



4th. Valvular insufiiciency of the left heart and tumors or 

 aneurisms interfering with circulation through the aorta, cause 

 passive congestion of the pulmonary veins and oedema of the lung. 



5th. Tumors and diseases of the liver determine passive con- 

 gestion of the portal system and ascites. 



6th. Passive congestion is very liable to take place in an organ 

 the functions of which are impaired as in a paralyzed part. In 

 this the hypersemia may start in the capillaries and extend to the 

 veins or even to the arteries. 



