266 DISEASES OF THE HORSE. 



atheroma, degeneration, and dilatation of tlie mesenteric arteries, 

 associated with thrombus and aneurism. The aneurism gives rise to 

 colic, which appears periodically in a very violent and often persis- 

 tent type. Ordinary colic remedies have no effect, and after a time 

 the animal succumbs to the disease. In all cases of animals which are 

 habitually subject to colicky attacks, parasitic aneurism of the an- 

 terior mesenteric artery may be suspected. (See p. 92.) 



Pathology. — Aneurisms may be diffuse or sacculated. The diffuse 

 consists in a uniform dilatation of all the coats of an artery, so that it 

 assumes the shape of a cjdindrical swelling. The wall of the aneu- 

 rism is atheromatous, or calcified ; the middle coat may be atrophied. 

 The sacculated, or circumscribed, aneurism consists either in a dila- 

 tation of the entire circumference of an artery over a short portion 

 of its length, or in a dilatation of only a small portion of one side of 

 the wall. Aneurism may become very large ; as it increases in size it 

 presses upon and causes the destruction of neighboring tissues. The 

 cavity of the aneurismal sac is filled with fluid or clotted blood or 

 with layers of fibrin which adhere closely to its wall. Death is pro- 

 duced usually by the pressure and interference of the aneurism with 

 adjoining organs or by rupture. In worm aneurism we usually find 

 large thrombi within the aneurismal dilatation of the artery, which 

 sometimes plug the whole vessel or extend into the aorta. Portions of 

 this thrombus, or clot, may be washed away and produce embolism of 

 a smaller artery. The effect in either case is to produce anemia of the 

 intestinal canal, serous or bloody exudation in its walls, which leads 

 to paralysis of the intestine and resultant colicky symptoms. 



Treatment. — The only treatment advisable is to extirpate or ligate 

 the tumor above and below. 



RUPTURE OF AN ARTERY. 



Endarteritis, with its subsequent changes in the walls of arteries, is 

 the primary cause of rupture in the majority of instances. The rup- 

 ture may be partial, involving only one or two coats, and will then 

 form an aneurism. If complete, it may produce death when it in- 

 volves a large vessfel, especially if it is situated in one of the large 

 cavities permitting an excessive escape of blood. Rupture may be 

 produced by mechanical violence or accident. 



Symvtoms. — In fatal rupture, associated with profuse bleeding, 

 the animal becomes weak, the visible mucous membranes become 

 blanched, the breathing hurried or gasping, pupils dilated, stagger- 

 ing in gait, syncope, death. When the hemorrhage is limited the 

 symptoms may not become noticeable; if it is near the surface of 

 the body a round or diffuse swelling or tumor may form, constituting 

 a hygroma. If the rupture is associated with an external woimd, 

 the bleeding artery should be ligated, or where a bandage is ap- 



