584 DISEASES OF THE ARTERIES AND LYMPHATICS. 



time, and removed by absorption, without causing the ulceration 

 which follows the common thread suture. 



The changes that occur in an artery after it has been tied are 

 as follows : — Plastic exudation takes place from the extremities 

 of the middle and inner coats at the line of deliqniation, with 

 exudation into the areolar tissue surrounding the artery. Its 

 different coats can no longer be distinguished ; and sooner or 

 later, by means of a thin exudation of lymph exterior to the 

 portion of coagulum formed by the coagulation of the blood, the 

 walls of the artery and the surrounding areolar tissue become 

 condensed into one mass, in which original parts can no longer 

 be distinguished ; and by the organization of this exudation into 

 fibrous tissue the artery becomes permanently obliterated. 



THE "DISSECTING ANEURISM," 



Is fortunately a rare variety even in the human being. This 

 form of aneurism is due to rupture of the internal and middle 

 coats of the artery, which allows the blood to escape outwards 

 and to burrow under the external coat, separating it from the 

 middle coat, so as to form a cavity, extending in some cases for 

 a considerable distance in the course of the vessel, and involving 

 more or less of its circumference. It is generally met with in 

 the aorta, and is a cause of much agony. 



Aneurism of a large artery, such as the aorta or mesenteric, 

 may cause sudden death by rupture of the arterial coats ; the 

 symptoms being those common to all excessive hsemorrhages, 

 namely, rapid sinking of the vital powers, paUor of the mucous 

 membranes, coldness of the surface of the body, extremities, 

 and mouth, — the animal generally, before dying, emitting a 

 peculiar shriek of agony. 



FALSE ANELT^ISMS. 



Traumatic or false aneurisms may be diffuse or circumscribed. 

 In the diffuse the blood becomes extravasated in the tissues, 

 forming a sort of flattened mass over the vessel, which com- 

 municates to it a feeling of pulsation. 



In the circumscribed, the areolar tissue surrounding the 

 opening in the artery becomes condensed, so as to form a sac 

 wliich limits the etlused blood. 



