Some have supposed that old age, and the deposit of earthy material which is formed in the arteries at that period, are predisposing causes of aneurism ; yet, if this was the case, the disease should be very prevalent indeed among those advanced in life, whereas it is in reality almost as rare as in infancy or early youth. Of fifteen cases of large aneurism operated on, only two had exceeded the age of forty years, the average of all being but thirty-one and a half ; and if a larger number of cases (inclusive of the internal forms of the disease) were collected and compared, it would probably be shewn to be considerably less. With respect to the earthy deposit alluded to, it is found between the fibrous and internal coats closely adhering to the latter, from which it can scarcely be separated : it is disposed in thin laminae or plates of different sizes, the largest being seldom greater than a spangle, and these earthy spots are distinct and separate, not running into or connected with each other, and never encircling the vessel with an un interrupted bony ring. They are supposed to render an artery friable and brittle, and there fore to predispose to aneurism, and have been considered by some to be the products of arterial inflammation. Unfortunately the origin and progress of this earthy degeneration have not yet been satisfactorily traced. Scarpa'" seems to regard it as arising from the same cause that produces the steatomatous deposit, and states that it cannot be said to be proper to old age, as it is sometimes met with in patients who are not much advanced in life. I have seen these earthy depositions in the aorta of a female not twenty-five years of age, which was also highly inflamed and covered with spots of soft steatomatous deposit, but still that is far from proof of its being the product of active inflammation, or of its rendering the artery weak or disposed to aneurism.
Of any number of subjects above the age of sixty brought into a dissecting-room, three fourths will be found with this earthy dege neration in some of the arteries, .yet the in frequency of aneurism amongst old patients has been already remarked. Again, this de posit has been seen in the sac of a true aneu rism, a circumstance that would spew it did not greatly interfere with the distensibility of the arterial tunics or render them more friable, and, lastly, a large and important vessel in this condition has been tied without its beimg crushed or broken down short, and being fol lowed by consecutive haemorrhage. From these observations some reasonable doubt may be entertained of these deposits being the result of inflammation, more particularly as, at the period of life alluded to, there is an evident disposition to the formation of earthy deposits in many structures and organs as well as in the arteries.
When a large aneurism runs its course with great rapidity, an opportunity is frequently afforded of observing a condition of the vessel most favourable to the production of the dis ease, and which therefore may be considered as one of its direct or immediate causes. The
vessel in this case, on being slit up, exhibits its internal lining membrane less smooth and polished than in its natural state; its colour is changed to a deep roseate carmine, and it sepa rates from the subjacent fibrous coat with com parative facility. This latter structure is also changed in colour, but not to so bright a red as the other. Between these coats, but more closely attached to the internal, (for they peel off with it,) are numerous specks of a soft steatomatous material of a white or pale grey colour, presenting, on a superficial inspection, somewhat of the appearance of the calcareous deposit already spoken of. An artery in this condition has lost more or less of its elastic properties; it is distended, and its calibre increased equally around. As the arteries are always full, the impulse of every new wave of blood driven on the greater quantity con tained within the distended vessel increases its apparent pulsation, for it is in the diastole or expanded condition of the artery that the pulse is felt. This loss of elasticity must obviously weaken the vessel, and cause it to be less re sisting: a fact that can be proved by expe riment after death, when an artery so circum stanced will be found to yield and tear under a distending force that would have little effect on it if in health, and will explain how an apparently trifling exertion may produce aneu rism in one man, whilst numbers of others exposed to similar or even greater violence escape safe and unharmed.
If arteritis can be justly considered as an immediate cause of aneurism, it follows that any thing tending to produce this condition of the vessel will predispose to the disease. An investigation of the natural history of this affection would, therefore, prove equally useful and interesting, but as yet a sufficient num ber of facts have not been collected from which any useful practical induction can be drawn. The experience of an individual cannot be sufficient to establish a fixed and general posi tion, but may be valuable if it induces others to a similar line of investigation, in order to its being verified or contradicted ; and from a minute attention to the previous history of several cases, I have frequently been able to connect intemperance, particularly in the use of spirituous liquors and repeated or ill-con conducted courses of mercury, with the pro duction of arteritis. how far these can explain the comparative infrequency of the disease in females and its prevalence amongst men sub ject to exposure, and too often of reckless and dissolute habits, must be determined by future observation ; but, in corroboration of the latter part of this opinion, it may be remarked, that few old persons are subjected to a course of mercury that do not perish shortly after by the bursting of a bloodvessel,—of apoplexy, or hzemoptoe most frequently.