Ligatures composed of animal substance, such as catgut, have been proposed as preferable to all others, on the supposition that they would be absorbed, and occasion less irritation; the fallacy of any such theory has already been adverted to. After the ligature has been applied for some time, it induces ulceration of the external coat which it envelopes, by which means it becomes detached from the vessel; acting as a foreign body, and causing a slight degree of suppuration, it makes its way by nature to the surface and is discharged. The period at which it separates may be said to be from the tenth to the twentieth day; sometimes sooner, seldom later. If, however, much of the surrounding parts have been extensively included along with the vessel, a longer period will probably elapse before the separation of the ligature. One end only of the ligature should be cut away close to the artery, the other being left hanging from the external wound; perhaps it is even safer to leave both, unless a third knot is made upon it; thus the extraneous body, when detached, can be gently pulled at so as to hasten the separation: this must be done with very great caution. When both ends are cut short, and the knot closed in, there is a risk of secondary hemorrhage, from the ligature causing formation of matter round it, perhaps detaching the vessel from its connections, and causing ulceration of its coats. The operation ought to be performed at as early a period of the disease as possible. Some recommend that it should be delayed in recent cases, with the view of allowing sufficient time for the anastomosing vessels to enlarge, in order that the circulation may be more vigorous in the smaller branches after obstruction of the principal vessel. Such delay prolongs the patient’s sufferings, which are in many cases extremely acute, and the precaution is altogether unnecessary, as has been amply proved by experience. On the same principle, the previous application of pressure to the vessel has been recommended; but few surgeons, if any, are now afraid of trusting to the resources of Nature when the principal vessel of a limb is obliterated, and that suddenly, without previous dilatation of the anastomoses. Cases are on record, in which the abdominal aorta has been completely obstructed by a natural process, without much impeding the inferior circulation; and in one remarkable instance of this description, the inconvenience was so slight that the disease was not suspected during the life of the patient, the lower limbs retaining their usual size and activity. In plethoric habits it may sometimes be prudent to abstract blood, even more than once, previously to the operation.