DISEASES OF THE ARTERIES. 243 



first, little is known during life, for all the symptoms which they pro- 

 duce may arise from other causes. Aneurism of the anterior aorta 

 may be situated very closely to the heart or in the arch, and it is very 

 seldom that we can distinguish it from disease of the heart. The 

 tumor may encroach upon the windpipe and produce difficulty in 

 breathing, or it may produce pressure upon the venae cavse or the 

 thoracic duct, obstructing the flow of blood and lymph. In fact, 

 whatever parts the aneurism may reach or subject to its pressure, may 

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

 chest is large, we generally find much irregularity 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 without any evidence of lung affec- 

 tion. Sometimes pulsation of the tumor may 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 over- 

 looked, affecting the anterior mesenteric artery, primarily induced by 

 a worm Strongylus vulgaris. This worm produces an arteritis, with 

 atheroma, 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 an- 

 terior mesenteric artery may 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 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 aneurisihal 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 



