THIS is a Disease of the Arteries, in which, either by a preternatural Weakness of any part of them, they become excessively dilated; or by a Wound through their Coats, the Blood is extravasated amongst the adjacent Cavities. The first Species of Aneurism is incident to every part of the Body, but does not often happen, except to the Curvature of the Aorta, which is subject to this Disorder from the extraordinary Impulse of the Blood on that Part from the Curvature, it runs upwards along the Carotids or Subclavians, generally increasing, 'till by its great Distension it is ruptured, and the Patient dies.

There have been great Disputes amongst Writers, concerning the Nature of this Dilatation of the Artery; some even denying the Fact, and supposing it always a Rupture; some, that all the Coats are distended; others, only the external one; and again others, whose Doctrine has been the best received, that the internal Coat was ruptured, and the external dilated: These last have supported their Hypothesis with Arguments drawn from the Anatomy of the internal Coat, which is ligamentous and incapable of much Distension; so that if an Artery be inflated with a sufficient force, the Air will burst that Coat, and expand the external one, that is, make an artificial Aneurism, in the same manner as Blood is supposed to make a natural one: But this Argument is of little force, when we consider, that there are many parts of an animal Body, which Violence cannot stretch considerably, but which, by the gradual Influx of the Juices, become susceptible of monstrous Distension, as is the Case of the Uterus, and upon Observation, is evidently the Case likewise, of all the Coats of the Artery, as I have had an Opportunity to examine in several Aneurisms in the Collection of the late Dr. Douglas, which he was so kind to lend me for that purpose.

There are several Histories given of Aneurisms of the Curvature of the Aorta, in some of which, the Vessel has been so excessively dilated as to possess a great space of the upper Part of the Thorax; and the most curious Circumstance to be gathered from them is, that the Spot of the Vessel which is weakest, and where the Disease begins, generally gives way in such a manner to the force Of the Blood continually pushing it outwards, as to form a large Pouch or Cyst, with Coats nearly as thick as those of the Artery itself: However, the Thickness of the Coats of these Cysts will last but to a certain Period; for when the Vessels of the Coats can no longer conform to the Extension, the Circulation grows Ianguid, the Cyst becomes thinner at its Apex, and soon after, bursts.

From this Description of the Cyst, it will be understood to resemble the Bladder, having a large Cavity, and a narrow Neck or Opening.

The Symptoms of this Aneurism, are a strong Pulsation against the Sternum and Ribs every Systole of the Heart; and when it extends above the Sternum, a Tumour with Pulsation: Upon Dissection, the Ribs, Sternum, and Clavicle, are sometimes found carious, from the Obstruction of the Vessels of the Periosteum, which are pressed by the Tumour. What are the Causes of a particular Weakness in any of the Coats of the Artery, I cannot take upon me to determine: but 'tis worth observing, that the dilated Aorta everywhere in the neighbourhood of the Cyst, is generally ossified; and indeed Ossifications, or Indurations of the Artery, appear so constantly in the beginnings of Aneurisms of the Aorta, that 'tis not easy to judge, whether they are the Cause or the Effect of them.

What I have spoken of hitherto, has been only the Aneurism of the Thorax from an internal Disorder; Aneurisms of the Extremities, are for the most part owing to Wounds, though when they happen of themselves, they differ very little from the Description I have given of that in the Thorax: The further Symptoms of them are (besides Pulsation) the Tumour's being without Discolouration in the Skin; its subsiding when pressed by the Hand, and immediately returning when the Hand is taken away; though if it be upon the point of bursting, the Skin will grow inflamed, and the coagulated Blood in the Cyst will sometimes make the Pulsation much less perceptible.

This Species of Aneurism may sometimes be supported a great number of Years, if we resist its Dilatation by proper Bandage; but if we do not, there is danger of its bursting; and if it be pretty large, of rotting the adjacent Bones.

A sound Artery wounded through part of its external Coat, would in all probability produce nearly the same Appearances as where the whole Coat is weakened from an internal Indisposition; and this most likely is the case after bleeding in the Arm, when it has not been immediately perceived that the Artery was pricked, and the Tumour has begun to form some Days after the Puncture; though the common Appearance of an Aneurism from the Wound of a Lancet, is a Discharge of Blood first through the Orifice of the Skin, and, upon being stopt from bleeding outwardly, an Insinuation of it among all the Muscles as far as it can spread in the Shoulder and Arm: here, the Arm grows livid from the Ecchymosis, and the Blood coagulating to the consistence of Flesh prevents any sensible Pulsation. The Cyst which arises near the Orifice of the Artery is formed by the Cellular Capsula enveloping the Vessels of that Part, and a portion of the Aponeurosis of the Biceps Muscle, which admitting of some extravasated Blood underneath it, become excessively thickened and expanded: These Membranes must make the Cyst, otherwise, we could not upon opening the Tumour in the Operation, discover so readily the Puncture; or if the Coats of the Artery Made it, we could not separate it distinctly from the Vessel, which would be always dilated above and below the Cyst, as we see in other Aneurisms.

There are some few Instances of small Aneurisms and Punctures of the Artery from Bleeding, doing well by Bandage; but they almost all require the Operation at last, which is to be performed nearly in the same manner in every part; and supposing it in the Bend of the Arm, is to be done after the following Method.

Having applied the Tourniquet near the Shoulder, and laid the Arm in a convenient Situation, make an Incision on the Inside of the Biceps Muscle, above and below the Elbow a considerable length, which being in the course of the Artery, will discover it as soon as you have taken away the coagulated Blood, which must be all removed with the Fingers, the Wound being dilated sufficiently for that purpose: If the Orifice does not readily appear, let the Tourniquet be loosened, and the Effusion of Blood will direct you to it; then carefully carrying a crooked Needle with a Ligature under it, tie the Vessel just above the Orifice, and passing the Needle again, make a second Ligature below it, to prevent the Return of the Blood, and leave the intermediate piece of the Vessel to slough away without dividing it, To avoid wounding or tying the Nerve in making the Ligature, the Artery may be cleared away from it first, and held up with a Hook; but should the Nerve be tied with the Artery, no great Inconvenience would ensue from it. After the Operation, the Arm must be laid easy, on a Pillow in Bed, and the Wound be treated in the common Method, keeping it in that Posture a Fortnight or three Weeks, especially if it should swell much, and not digest kindly.

In doing this Operation, it will be proper to have the amputating Instruments ready, lest it should be impracticable to tie the Artery (though I have never met with such an Instance) and even after having tied it, the Arm must be carefully watched; that in case of a Mortification it may be taken off; which though from Experience we learn is very seldom the Consequence, should to all appearance be the perpetual one; for these Aneurisms, following always upon bleeding the Basilic Vein, must necessarily be Aneurisms of the Humeral Artery, near an Inch above its Division, which being obstructed by the Ligature, one would think, should necessarily bring on a Mortification; but we see the contrary, though for some time after the Operation, we can hardly distinguish the least degree of Pulse, and ever after it continues languid. If the Humeral Artery happens to divide above the Elbow, which is not very uncommon, the Prospect of Cure is better, and the Pulse will be stronger after the Operation.