PRINCIPLES OF VETERINARY SURGERY 73 



the seat of a copious transudation of serum into the tissue- 

 spaces. The passive hyperaemia may be local or general. In 

 local oedema only a small vein is obstructed and the svi^elling 

 remains limited to the tissues directly concerned. But often 

 a circumscribed oedema may spread from the pressure it 

 itself exerts upon neighboring veins. Thus a trivial swelling 

 of the abdomen may become an enormous oedema of the 

 entire ventral surface of the body. The local cedemas ob- 

 served in animals are caused from inflammatory swellings 

 which press upon veins, solution in the continuity of veins 

 in accidental or surgical wounds, ligation of veins, pressure 

 of tumors, venous emboli, pressure of bandages, and in fact 

 any condition that is capable of retarding the free backward 

 flow of venous blood from any given tissue. Thus a bruise 

 to the forearm, by interfering with the upward movement of 

 blood in the radical veins, will promptly cause a pronounced 

 oedema of the entire limb below. In the same manner a dis- 

 ease of the liver will cause ascites by hindering the flow of 

 intestinal blood through it. 



General oedema is due to tricuspid insufficiency, obstruc- 

 tion of the venae cavse, or general depression of the circula- 

 tory apparatus. When the tricuspid fails to efifectually close 

 the right auriculo-ventricular opening with each contraction 

 of the right ventricle the inward flow of venous blood into 

 the right auricle is retarded. The entire venous current from 

 the remotest capillaries feels the effect of the added obstacle 

 to its already difficult passage from the periphery to the 

 heart, and the result is a transudation of serum at different 

 parts of the body. A general dropsy may thus be provoked. 

 When the obstruction is but partial the total effect may be 

 an oedema of the tegs, where gravity greatly hinders the 

 return current. If the circulation is depressed from disease 

 or overwork, gravity alone may be sufficient to determine an 

 obstinate oedema of the hind legs. The arterial blood may 



