When arteritis has proceeded to the extent of producing these steatomatous deposits, if aneurism is not inevitable, it is certainly very likely to ensue. In some instances the loss of elasticity is so great as to cause all the coats of the vessel to yield and become distended into the sac of a true aneurism : in others, (and far more frequently) the process of ulce ration commences, the lining membrane cover ing one of these spots first becoming soft, then exhibiting a distinct ulcer which proceeds from within, eroding the middle coat either through its entire thickness to the cellular, which is then easily distended into the aneu rismal sac ; or so far as that it shall be likely to give way and tear under a trifling shock, even under the impulse of the circulation. In the pathological collection of the medical school of Park-street, Dublin, there are pre parations exhibiting these forms of aneurism and the different stages of dilatation, of soft ening, and of ulceration in the most satisfactory manner.
Circumscribed false aneurism. When a person experiences a sensation as if something had given way or been torn within his limb, or even without such previous warning, per ceives a small hard, pulsating tumour situated somewhere immediately on the course of a large or leading artery, it is to be suspected that an aneurism has formed. And this suspicion is confirmed, if the tumour becomes larger or smaller, according to the diastole or systole of the artery, or is diminished by pressure, or almost disappears if the patient should happen to faint. If pressure be applied on the trunk of the artery between the tumour and the heart, its pulsation ceases, its size is sensibly diminished, and it becomes soft and flaccid ; if on the farther or distal side of the tumour, its size is increased, and its throbbing rendered far more evident. The pulsation is said to become more faint in proportion to the growth of the tumour, and this, though generally true, is not so universally, for this symptom will presently be found to be influenced by a num ber of circumstances, such as the blood within the sac being fluid or coagulated, the situation and depth of the tumour within the limb, and the coverings of fascia it may possess. In most instances there is a peculiar whizzing sound, plainly perceptible on applying the ear or a stethoscope to the tumour, termed by the French the " bruit de soufflet;" but its pre sence or absence is by no means pathogno monic, foi it may be artificially produced by pressure on the trunk of any large artery.
On examining a circumscribed aneurism after death or the removal of the limb, the artery should, if possible, be always slit up on the side opposite to that from which the tumour springs. The appearances of inflam mation will probably depend on whether the aneurism be recent or of long standing, and obviously on whether it has been the result of accident or disease. Also, if it be recent, the aperture leading into the sac is generally well defined, circular, and circumscribed, its edges remarkably thin and fine: if, on the contrary, it is old, the aperture is large, smooth, and so even as to present an appearance as if the lining membrane had been prolonged from the artery into the sac. On cutting into the sac
some fluid blood is usually found, and always a quantity in a state of coagulation. Besides, there is always more or less of fibrine, the remains of former coagula deposited in irre gular laminae, and varying in colour from a pale red or grey. The most external layers are closely fastened to the internal wall of the sac by means of large depositions of flaky lymph, from which, however, they can be separated by careful washing or maceration. This lymph thickens the walls of the sac, and imparts to them considerable firmness and resistance. The sac, itself, is most generally of an oval form, but to this there are some exceptions, amongst which the occasional oc currence of a dissecting aneurism is the most curious. This happens when the internal and middle coats having ulcerated or given way, the blood insinuates itself between the fibrous and cellular coats, detaching them from each other to a considerable extent, whence the dis ease has derived its name.* Such is an outline of the appearances on dissection, but they will avail little in explaining the nature of aneu rism, unless combined and compared with the phenomena of the disease during life.
And, in the first instance, it must be recol lected that the tumour is pulsatile, a quality that proves the entrance of a quantity of fluid blood, and its return back again into the artery by the resistance or reaction of the sac. It was this circumstance that principally led Fer nelius to believe and to teach that aneurism consisted in a dilatation of all the coats of the artery, inasmuch as he could not understand how pulsation occurred if the tumour did not possess an elastic covering, and moreover imagined that if the blood was driven into a sac otherwise constituted, it must of neces sity remain there and become coagulated. It is, however, unnecessary now to discuss the question as to whether the sac of an aneurism possesses elasticity or not, when it is daily observed that any tumour (an enlarged gland for instance) situated on an artery, and re ceiving an impulse from the heart, may com municate the sensation of pulsation, provided the skin and other elastic tissues covering it are sound. Nay, farther, it may be remarked that the pulsation of an artery, even with its elastic coat uninjured, is much more apparent than real, and when felt ab externo, is greatly influenced by the skin and its other coverings. It is a fAct too well known to every operating surgeon to be for a moment controverted, that an artery when exposed exhibits nothing like the force. of pulsation that it did before the skin was divided ; sometimes it is difficult to ascertain it satisfactorily at all. The late Pro fessor Todd has strongly pointed out this circumstance in his case of axillary aneurism, published in the third volume of the Dublin Hospital Reports, where he says, " For some time I could not be convinced that the feebly pulsating vessel, to which the point of my finger was applied, was really an artery of such magnitude as the subclavian ;" and similar observations could be adduced, if necessary, from other sources.