In practice, a ligature is applied around an artery under two different circumstances; one, in the case of the wounded and bleeding artery, it is placed on the open orifice of the vessel ; the other, in the treatment of aneurism, the artery is taken up and tied at a part where it is supposed to be sound and uninjured. When, in either of these cases, an artery is tied, the first effect is obviously to bring its opposite sides into apposition, and to arrest the flow of blood through it. At the same time that the internal and fibrous coats being shorter and less tough yield under its pressure and are divided completely, leaving the cellular coat entire, still sustaining the ligature in its place. The consequences of this division of the internal coats are very similar to those already explained • as following the complete section of the artery ;.
there is the same effusion of lymph, the for mation of internal coagulum of the same conical shape and to the same extent, the diversion of the circulation through the collateral branches, and if the case proceeds favorably, the ultimate obliteration of the tube between the place occupied by the ligature and the next anasto mosing branch. But the ligature is still to be attended to. The portion of the cellular coat included within its noose sloughs and dies, and is to be detached from the remainder by the absorption of the adjacent sound part. This process takes place at different periods of time according to the size of the vessel ; it separates from the subclavian about the twenty second day after the operation,from the femoral about the sixteenth, and from the brachial so early as the twelfth or fourteenth. Unfor tunately matters do not always proceed thus favorably, and the separation of the ligature is the commencement of a series of evils to the patient and of embarrassment to the surgeon, that can scarcely be paralleled in the practice of surgery. It has been found, however, by experience, that a ligature placed on an artery that has been fairly divided, is more rarely followed by those ill consequences that fre quently ensue when its continuous tube is tied, and as this latter operation is so intimately connected with the subject of aneurism, and as it will be necessary to become acquainted with the phenomena of inflammation in these struc tures, in order to understand those of secon dary or consecutive haemorrhage, this part of the subject cannot at present be so favorably discussed.
Morbid states of arteries. Aneurism.— Aneurism (ayEvew-p,oc, vel is a term of such extensive application as to pre clude the possibility of an accurate definition.
It has been employed by Corvisart and others to designate certain affections of the heart, but is now most generally used to express a disease produced by a dilatation of an artery, or by solution of one or all of its coats. It is also applied to any distended condition of a part of the vascular system, such as occurs when an unnatural communication is formed between an artery and vein, constituting the diseases of aneurismal varix and varicose aneurism. The name of aneurism by anastomosis has also been given to those bloody tumours, which, at first appearing only as marks or stains occa sioned by a congeries of vessels, increase either with the growth of the individual, or according as the vascular system may be accidentally ex cited, until finally they produce results of a most formidable description. • Aneurisms have been classed, first, as to the condition of the coats of the artery, a dilata tion of them being considered as the true aneu rism, whilst a rupture or ulceration of them constitutes the false : and, secondly, as to the condition of the effused blood, which, if it is contained within a sac or bag, constitutes the circumscribed 'form of the disease, or if it has been poured out throughout the circumjacent cellular tissue, forms the diffused aneurism. The nature of aneurism, however, will be better understood by considering it to consist of such a lesion of an artery as will permit the passage of a portion of the blood out of the usual course of the circulation, though not out of the vicinity of the injured or diseased vessel, and according to the different circumstances under which this can occur, the disease will be found to arrange itself under the following distinct species. In the first four of these the effused blood is either partially or entirely withdrawn from the circu lation, and becomes coagulated in its new situation : in the others it passes from the usual course of the circulation, but is not withdrawn entirely from it, and consequently does not coagulate.
1. Where by rupture or ulceration of the internal and middle coats of the vessel, the blood is propelled against the external cellular coat, which becomes thus distended into a pouch containing within it the extravasated blood, in a more or less perfect state of coagulation, which pouch is termed the aneurismal sac. This is circumscribed fidse aneurism.