242 BUKEAU Oi' ANIMAL INDUSTRY. 



or less degree. It is most frequently found in the arteries, although 

 the veins may develop an atheromatous condition when exposed to any 

 source of prolonged irritation. Athei'oma may effect arteries in any. 

 part of the body; in some instances almost ever}' vessel is diseased, in 

 others only a few, or even parts of one vessel. It is a very common 

 result of endocarditis extending into the aorta, which Ave find perhaps 

 the most frequent scat of atheroma. As a result of this condition the 

 affected vessel becomes impaired in its contractile power, loses its nat- 

 ural strength, and in consequence of its inability to sustain its accus- 

 tomed internal pressure, undergoes, in manv cases, dilatation at the 

 seat of disease, constituting aneurhm. In an atheromatous vessel, cal- 

 careous deposits soon occ;ur, which render it rigid, brittle, and subject 

 to ulceration or rupture. In such vessels the contractility' is destroyed, 

 the middle coat atrophied and be3'ond repair. Atheroma in the ves- 

 sels of the brain is a frequent cause of cerebral apoplexy. No symp- 

 toms are manifested bv which we can recognize this condition during 

 life. 



COXSTRICTTOX OF AN AIJTEEY. 



This is usually the result of arteritis, and ma}' partly or wholly be 

 impervious to the flow of blood. When this occurs in a large vessel 

 it may be followed by gangrene of the parts; usually, however, col- 

 lateral circulation will ])e esta])lished to nourish the parts previously 

 supplied by the obliterated vessel. In a few instances constriction of 

 the aorta has produced death. 



ANEURISM. 



Aneurism is usually dcscrilied as true •aw^ false. True aneurism is a 

 dilatation of tlie coats of an artery over a larger or smaller pai't of its 

 course. Such dilatations are usually due to chronic endarteritis and 

 atheroma. False aneurism is formed after a puncture of an artery by 

 a dilatation of the adhesive lymph by which the puncture was united. 



Symptoms. — If the aneurism is seated along the neck or a liml) it 

 appears as a tumor in the course of an artery and pulsating with it. 

 The tumor is round, soft, and compressible, and yields a peculiar 

 fluctuation upon pressure. By applying the ear over it a peculiar 

 purring or hissing sound may sometimes be heard. Pulsation, syn- 

 chronous with the action of the heart, is the diagnostic symptom. It 

 is of a slow, expansive, and heavy character, as if the w hole tumor 

 were enlarging under the hand. Aneurisms seated internally may 

 occupy the cavity of the cranium, chest, or abdomen. As regards the 

 first, little is known during life, for all the symptons 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 



