When digital compression is not available, the most convenient and certain means of preventing hæmorrhage--say in an amputation--is by the use of some form of _tourniquet_, such as the elastic tube of Esmarch or of Foulis, or an elastic bandage, or the screw tourniquet of Petit. Before applying any of these it is advisable to empty the limb of blood. This is best done after the manner suggested by Lister: the limb is held vertical for three or four minutes; the veins are thus emptied by gravitation, and they collapse, and as a physiological result of this the arteries reflexly contract, so that the quantity of blood entering the limb is reduced to a minimum. With the limb still elevated the tourniquet is firmly applied, a part being selected where the vessel can be pressed directly against a bone, and where there is no risk of exerting injurious pressure on the nerve-trunks. The tourniquet should be applied over several layers of gauze or lint to protect the skin, and the first turn of the tourniquet must be rapidly and tightly applied to arrest completely the arterial flow, otherwise the veins only are obstructed and the limb becomes congested. In the lower extremity the best place to apply a tourniquet is the middle third of the thigh; in the upper extremity, in the middle of the arm. A tourniquet should never be applied tighter or left on longer than is absolutely necessary. The screw tourniquet of Petit is to be preferred when it is desired to intermit the flow through the main artery as in operations for aneurysm. When a tourniquet cannot conveniently be applied, or when its presence interferes with the carrying out of the operation--as, for example, in amputations at the hip or shoulder--the hæmorrhage may be controlled by preliminary ligation of the main artery above the seat of operation--for instance, the external iliac or the subclavian. For such contingencies also the steel skewers used by Spence and Wyeth, or a special clamp or forceps, such as that suggested by Lynn Thomas, may be employed. In the case of vessels which it is undesirable to occlude permanently, such as the common carotid, the temporary application of a ligature or clamp is useful. #Arrest of Hæmorrhage.#--_Ligature._--This is the best means of securing the larger vessels. The divided vessel having been caught with forceps as near to its cut end as possible, a ligature of catgut or silk is tied round it. When there is difficulty in applying a ligature securely, for example in a dense tissue like the scalp or periosteum, or in a friable tissue like the thyreoid gland or the mesentery, a stitch should be passed so as to surround the bleeding vessel a short distance from its end, in this way ensuring a better hold and preventing the ligature from slipping. If the hæmorrhage is from a partly divided vessel, this should be completely cut across to enable its walls to contract and retract, and to facilitate the application of forceps and ligatures.