192 ON THE NATURE AND PRINCIPLES OF 



result of arterial disease. It is true that we occa- 

 sionally find great dilatation of the whole tube near 

 its attachment to the heart, but it would appear 

 almost a physical impossibility that any amount of 

 lateral pressure which the arterial blood might derive 

 from the ventricular impulse could, in the natural 

 state of the aortic coats, induce their laceration. In 

 cases, however, where their strength and elasticity- 

 have been diminished by previous disease, this force 

 may and does occasion their rupture at the weakened 

 points, and thus becomes the immediate cause of 

 aneurism. And the same dilating pressure continu- 

 ing to act upon the attenuated coats of the aneu- 

 risinal sac, induces that laceration which generally 

 conducts these cases to a fatal issue. 



But, in addition to its well-known action as the 

 immediate or proximate cause of aneurism, it is, I 

 think, almost certain that an habitual increase in the 

 pressure of the arterial blood exercises an important 

 influence in predisposing to that disease. And 

 statistical observations, by showing its more frequent 

 occurrence in men than in women, and the peculiar 

 liability to it of sailors and others whose occupation 

 requires violent and sudden muscular exertion, eon- 

 tribute, with the fact of its most generally appearing 

 during the prime of life, to give considerable support 

 to the opinion. As a predisposing cause of aneurism 

 this force may operate dircrffi/. by causing a certain 

 amount of fibrinous exudation through the lining 

 membrane of the aorta into the cellular space between 

 it and the middle coat; or it may indin-rfh/ occasion 

 the same efU-ct. through the nutritious vessels or 



