266 DISEASES OF THE HORSE. 
atheroma, degeneration, and dilatation of the 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 saeculated. The diffuse 
consists in a uniform dilatation of all the coats of an artery, so that it 
assumes the shape of a cylindrical 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 vessel, 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. 
Symptoms.—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 wound, 
the bleeding arterv should be Heated. or where. a handace ic an- 
