TOURNIQUET is a peculiar kind of bandage applied to a limb for the purpose of arresting the current of blood through its main artery. It is employed for this purpose in several cues, but especially in amputations of parts of the limbs, where large arteries have to be suddenly cut across. Before the invention of the tourniquet, surgeons used to constrict the limb with a simple tight bandage ; but although this plan may well be resorted to in an emergency, it not only produces excessive pain, but, by obstructing the current through the veins more than that tho arteries, produces an extreme engorgement of the limb, and in amputation permits severe hiemorrhage. A slight improvement in this plan was that of twisting pieces of wood under the band, and so gradually tightening it; but the first instrument formed on the principles of the tourniquet was invented by Jean Louis Petit in 1718. Since that time various changes have been introduced. but at present the construction of all tourniquets is nearly similar, i They consist of a very tough band, about an inch and a half wide, upon which there is a moveable leather pad, to be placed immediately over the artery on which it is desirable that the chief pressure should be applied. For this purpose, also, the surface of the pad must be directed towards the bone of the limb, that the artery may be pressed firmly against it. The rest of the band is passed round the limb, and is fastened by a buckle. It is tightened and loosened by means of a bridge of brass, which is capable of being elevated or la down by a screw passing through it, and at the ends of which there are two small rollers, around each of which the band is made to take a half turn. In use, the bridge and screw are placed on the opposite side of the limb to the pad.
The tourniquet is now not so generally used as formerly. Many surgeons prefer to have the artery compressed during an amputation by an assistant, because the tourniquet is not free from the objection of compressing the veins as well as the artery, and is liable to accidents which cannot be instantly repaired. An instrument of a superior character has also been invented by Signor Signoroni, a surgeon at Milan. It is composed of two arches of steel, connected by a hinge at one end, and each bearing at the other end a pad. By an Archimedes screw ingeniously placed at tho hinge, the pads can be approximated and separated like the ends of the blades of a pair of calippers, and can be immoveably fixed in any position. In use, one pad is put over the artery, and the other on the opposite part of the limb, and tho screw is worked till, in their tendency to approximate, the pads have sufficiently compressed the artery, upon which alone the pressuie is thus made to fall.
As already said, in an emergency, such as that of a wound of any of the large arteries of a limb, when medical aid is not near, the old fashioned tourniquet should be instantly applied. A piece of strong tape or cord should be tied in a double knot round the limb above the wound; a piece of wood, or anything firm, should be then passed under it, and twisted,just as packers tighten the cords round bales and boxes, till the flow of blood has ceased. For hteniorrhage from large veins or small arteries, this tourniquet should not be employed, but simple pressure with the finger or the hand.