420 DISEASES OF THE GREAT VESSELS. 



those next the blood are reddened and soft Here and there, between 

 their layers, there are frequently deposits of brownish-red or chocolate- 

 colored blood. 



The vessels proceeding from the sac, independently of the contrac- 

 tion to which they are liable by ossification, are not unfrequently 

 blocked up by clots of fibrin, and are impervious to blood. In other 

 cases, their mouths are stretched into narrow slits, and in others again 

 they may be narrowed or closed by pressure of the tumor. The con- 

 dition of the vessels springing from an aneurism is important in a diag- 

 nostic point of view. 



The size of aortic aneurism varies. Within the pericardium they 

 rarely attain any great magnitude, but soon give way. When they 

 originate beyond the pericardium, however, they may grow to the size 

 of a man's head. 



The effect of an aneurism of the aorta upon the parts about it de- 

 pends upon the amount of displacement and pressure which it inflicts. 

 The trachea, the bronchi, the oesophagus, the great vessels of the 

 thorax, or the nerves, may be dislocated or atrophied by the compres- 

 sion to which they are exposed. Atrophy, or " usur," of the bones 

 may even open the spinal canal, and destruction of the bone and carti- 

 lage of the thorax may permit the aneurism to emerge as a prominent 

 tumor, covered only by soft parts. 



As partial dilatation of the aorta augments the labor of the heart, 

 that organ is almost always hypertrophied. 



Spontaneous cure of an aortic aneurism, by complete solidification 

 of the sac by means of coagula and subsequent atrophy, is one of the 

 greatest of rarities. Other forms of spontaneous cure, which some- 

 times occur in peripheral aneurism, are impossible in the aorta. 



When death does not result from the effect of the tumor upon the 

 circulation, and its pressure upon neighboring organs, the aneurism 

 usually bursts spontaneously, a mode of termination vastly more fre- 

 quent than that by recovery. If it open into the pericardium, or 

 pleura, a genuine rupture at the thinnest point takes place ; if into the 

 O3sophagus, trachea, or one of the bronchi, it gives way at some point 

 of adhesion which forms between the tumor and one or other of these 

 organs, and which, gradually growing thinner, at last breaks ; or else a 

 slough forms and separates, thus making an aperture into the sac. 

 Opening into a neighboring vessel takes place after its walls have 

 become adherent, and communication is established by a gradual wast- 

 ing of the septum thus formed. More rarely, it is only the adventitia 

 of the vessel that becomes adherent, and, after perforation at the ad- 

 herent spot, blood is injected between the adventitia and media of the 

 vessel. The external rupture of an aneurism, which has penetrated 



