352 Veterinary Medicine. 



b. Changes in the vessels. Any disturbance or alteration of the 

 endotiielium sets free the so-called fibrine ferment, and precipi- 

 tates coagulation. Lister found that contact of ammonia with 

 the interior of an otherwise living vein caused a thrombus. So in 

 all endarteritis and phlebitis coagulation takes place on the serosa 

 and quickly blocks the vessel. Even in the capillary vessels the 

 same principle holds, and in inflammation minute coagula 

 (thrombi) form in the capillary network throughout the whole 

 inflamed area. This explains not only the capillary blood stasis 

 but the thrombosis of inflamed arteries and veins. In these two 

 latter the clot increases and extends in the direction of blood 

 stasis : — in the artery toward the heart as far as the next colateral 

 branch, and in the veins away from the heart as far as to the next 

 colateral trunk. On the distal side of the arterial thrombus the 

 blood flows off freely toward the capillaries, but on the proximal 

 or cardiac side it is absolutely stagnant up to the next branch 

 through which it can freely flow into the capillary plexus. Into 

 this stagnant blood the fibrine ferment, produced by the altered 

 white globules in the clot already formed, slowly extends until 

 the whole has formed a firm coagulum. Beyond this the actively 

 moving blood carries off and dilutes this ferment so rapidly that 

 it can exert no appreciable effect on the fibrine-forming elements. 

 The principle is an important one in surgery, as the clot formed 

 entad of the ligature will be extensive in proportion to the dis- 

 tance from the first colateral trunk, and in inverse proportion to 

 this clot will be the danger of secondary haemorrhage. In veins 

 the same rule holds, with this difference that as the blood is flow- 

 ing toward the heart it empties the vessel on the cardiac side, and 

 stagnates on the distal side up to the next colateral branch. 

 Hence it is that a thrombus in a vein always extends away from 

 the heart, while that of the artery extends toward it. 



Another cause of coagulation is the deoxidation of the blood 

 and the excess of carbon dioxide. This occurs in the stagnant 

 blood in the vessels and above all in the capillaries. The normal 

 trophic changes in the serosa, fail to take place in contact with 

 blood in this state, and the resulting changes in the white and 

 endothelial cells set free fibrine ferment and determine coagula- 

 tion. Stasis of the blood from any cause (ligature, pressure, em- 

 bolism), tends to this condition and the extension of the coagulum. 



