ANEURISM. 97 



one or more of the coats of the artery. The artery may be dilated, 

 all the coats being entire, as is usually the case in the aorta ; or,' 

 the internal and middle coats are ruptured, and the sac is formed of 

 the external coat. The interior of the sac is lined by fibrin in a 

 membranous form. 



False Aneurism. — Is owing to a complete division of the arterial 

 coats, either from a wound or external ulceration ; the sac is formed 

 in the cellular tissue. 



Dissecting Aneurism.— Is a sac formed by the infiltration of 

 blood between the coats of an artery. This sac may communicate 

 with an artery at several points. 



Circumscribed and diffused, are terms used to signify its limits ; 

 whether confined to a cyst, or extending by infiltration into the sur- 

 rounding tissues. 



Sij?npt077is.—The most frequent form of aneurism is the true cir- 

 cumscribed aneurism. The tumour, at first, is small, gradually 

 increasing, soft, and quite compressible, being only filled with fluid 

 blood. It has a distinct pulsation from the beginning, synchronous 

 with the heart's impulse, increased by pressure on the distal side, and 

 diminished or arrested by pressure on the cardiac side. A peculiar 

 thrill is imparted to the hand, which can be heard by application of 

 the ear. At first the pain is slight, and merely owing to interference 

 from the adjoining textures. By pressure upon the nerves a numb- 

 ness is produced; pressure on the veins and lymphatics causes 

 CEdema, discoloration, and swelling. The strength of the part is 

 much impaired, as the tumour enlarges ; the circulation in the ex- 

 tremity is weaker ; the diminished volume of the main artery is com- 

 pensated by enlargement of the side channels, the collateral circu- 

 lation conveying the blood from the cardiac to the distal side of the 

 tumour. The tumour gradually becomes larger by the separation of 

 fibrin, and is less compressible, and pulsates less distinctly. The 

 clot thus filling up the sac, restrains its further dilatation by the 

 force of the heart. Ultimately, it may become smaller by con- 

 tinued absorption. 



During the progress of an aneurism, adjacent parts are displaced, 

 altered, and absorbed, even bone is rendered carious and absorbed 

 by the constant pressure of the tumour. As the tumour enlarges, 

 pam and numbness increase, and the general health fails. At length 

 the tumour may burst, opening upon the skin or some important ca- 

 vity, and prove fatal, either by hemorrhage, or by pressure on impor- 

 tant parts,— as the trachea, oesophagus, &c., or by suppuration or 

 hectic. 



The diagnosis from abscesses, glands, and solid tumours is im- 

 portant. An aneurism is soft and compressible from the first, and 

 then becomes hard, whereas an abscess begins with induration and 

 ends with softening. A tumour or other swelling, receiving an 

 impulse from lying over the track of an artery, will no longer pulsate 



