DISEASES OF THE HORSE. 243 



tumor ma}^ encroach upon tne windpipe and produce difficulty in 

 ])reathing, or it may produce pressure upon the vens^ cavas or the 

 thoracic duct, obstructing the flow of blood and lymi^h. In fact, what- 

 ever parts the aneurism may reach or sul)ject to its pressure, ma}^ 

 have their fvmctions suspended or disturbed. When the tumor in the 

 chest is large, we generally lind much irregularit}- in the action of the 

 heart; the superficial veins of the neck are distended, and there is 

 usually dropsical swelling under the breast and of the limbs. There 

 may be a very troublesome cough Vv^thout anj- evidence of lung affec- 

 tion. Sometimes pulsation of the tumor ma}" be felt at the lower part 

 of the neck where it joins the chest. When the aneurism occurs in 

 the posterior aorta no diagnostic symptoms are appreciable; when it 

 occurs in the internal iliac arteries an examination per rectum will 

 reveal it. 



There is one form of aneurism which is not unfrequently overlooked, 

 affecting the anterior mesenteric arterj^, primarily induced bj^ a worm — 

 the Strongyhis annafiis. This worm produces an arteritis, with athe- 

 roma, degeneration, and dilatation of the mesenteric arteries, asso- 

 ciated with thrombus and aneurism. The aneurism gives rise to colic, 

 which appears periodically in a very violent and often persistent 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 anterior mesen- 

 teric artery ma}" be suspected. 



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 cylindrical swelling. The wall of the aneurism 

 is atheromatous, or calcified; the middle coat maj" be atrophied. The 

 sacculated, or circumscribed, aneurism consists either in a dilatation 

 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 la^^ers 

 of fibrin which adhere closely to its wall. Death is produced usually 

 by the pressure and interference of the aneurism with adjoining 

 organs or b}^ rupture. In worm aneurism we usually find large 

 thrombi within the aneurismal dilatation of the arter}^, which some- 

 times plug the whole vessel or extend into the aorta. Portions of this 

 thrombus, or clot, may be washed aAva}^ 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 colick}^ symptoms. 



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

 the tumor above and below. 



