[Illustration: Fig. 97.—Ring tourniquet.] When hæmorrhage has to be temporarily arrested, that of _Petit_ (fig. 98) is generally used. It consists of a strap of stout webbing and buckle, that can be rapidly tightened by a few turns of a screw. To use this tourniquet, lay a roller over the artery and carry the end once or twice round the limb to steady the roller, then pass the strap over the roller, keeping the buckle about two inches away from the screw and the screw on the anterior or outer aspect of the limb, not over the pad, lest that be displaced when the screw is tightened. The tourniquet should be screwed up as quickly as possible, that the limb be not charged with blood by obstructing the venous, before the arterial flow is checked. [Illustration: Fig. 98.—Petit’s tourniquet applied to the popliteal artery.] [Illustration: Fig. 99.—The horse-shoe tourniquet.] In _Signoroni’s Horse-shoe_ tourniquet (fig. 99) the extremities of the shoe can be approximated to each other by a rack screw working a hinge. The ends are furnished with pads, one broad and flat to bear on the limb away from the artery, the other rounded to compress the vessel itself. This tourniquet does not arrest the whole circulation in the limb. It can therefore be applied for a longer time than Petit’s. However, it easily slips out of place, and soon becomes very irksome and painful. [Illustration: Fig. 100.—Lister’s tourniquet for compressing the aorta.] _The Abdominal Tourniquet_ of Professor Lister is a very effectual contrivance for compressing the aorta during amputation through the hip joint, and operations where a tourniquet cannot be placed on the limb. It consists (see fig. 100) of a semicircular bar, with a broad pad to fit on the lumbar vertebræ behind, while in front it holds a long screw-pin carrying a pad. This instrument passes round the left side, and its pad is forced down into the abdomen, one inch to the left of the umbilicus, until the aorta is compressed against the spine. [Illustration: Fig. 101.—Carte’s tourniquets for femoral aneurism.]