418 DISEASES OF THE GREAT VESSELS. 



disease (Rokitansky), is questionable, at all events, as regards the 

 aorta, which is but poorly provided with contractile elements. 



In consequence of these changes, particularly in the middle coat, 

 the aorta loses its elasticity, sometimes at a circumscribed spot, some- 

 times throughout a larger portion of its extent, and gradually yields 

 and becomes dilated by the pressure of the blood. Not unfrequently, 

 however, upon the occasion of some sudden strain, the tunic of circular 

 fibres seems to give way suddenly, and the dilatation of the wall, which 

 now consists only of the adventitia and intima, goes on more rapidly. 

 Many persons suffering from aneurism believe that they know the 

 period, or even the moment, from which their malady dates, assigning, 

 as a cause, some violent muscular effort, the lifting of a heavy burden, 

 etc. It has already been remarked that a general contraction of the 

 muscles, by compressing many of the capillaries, must throw an in- 

 creased strain upon the aorta. A violent jar of the frame seems to 

 have a similar effect ; at least, many patients date their affection from 

 some fall from a great height, or the like. Such accidents will not 

 cause aneurism in a healthy subject ; and, in many cases, an acknowl 

 edgment of the immediate causes of the complaint is only forced upon 

 the patient by the examiner. 



Aneurisms are rare in young people. They occur chiefly in per- 

 sons of somewhat advanced age, in whom chronic inflammation of the 

 arterial coats is a very common affection. Men are much more fre- 

 quently attacked than women ; but as the majority of aneurisms are 

 found in persons who habitually make violent muscular efforts, this 

 difference may be accounted for by the difference in the occupations 

 of the sexes. 



ANATOMICAL APPEARANCES. Scarpctfs classification was mainly 

 based upon the number of coats which could be counted in the wall 

 of an aneurism. If the wall contained all three tunics, it was an 

 aneurisma verum ; if covered by the adventitia alone, it was an 

 aneurisma spurium, or mixtum externum. If, again, the wall con- 

 sisted of a protrusion of the intima through an opening in the media, 

 the pouch being either bare or covered by the adventitia, it was an 

 aneurisma mixtum internum seu Jierniosum. This classification has 

 been abandoned as unpractical. An aneurism may belong to the first 

 class (aneurisma vera) at the period of its commencement, and, as it 

 grows, become an aneurisma spuria ; and, indeed, in the same tumor, 

 one half of it may be of the true kind, and the other of the false. 



Classification of aneurisms, according to their form, is of more im- 

 portance. Thus we distinguish the circumscribed and the diffuse 

 aneurism. 



A diffuse aneurism involves a considerable portion of the vessel, 



