Salmon and Ody’s truss consists of a spring passing round the hip from a circular pad _b_, which bears on the sacrum to a second oval pad _a_. Both pads are attached to the spring by a ball and socket joint. There is also a slide for shortening or lengthening the spring if desired (fig. 111). This truss is worn round the _sound_ side of the body and reaches beyond the middle line to the hernial opening, with the object of directing the pressure of the spring outwards and backwards, or exactly counter to the course of the hernia inwards. [Illustration: Fig. 111.—Salmon & Ody’s truss.] _Umbilical hernia._—Spring trusses are not adapted for restraining umbilical hernia. The support consists of a broad belt fitted to the belly, made in front of elastic webbing, and on each flank, of white jean. Behind, the belt is fastened by straps and buckles, or by lacing, the better plan. In the centre, the elastic part carries a nearly flat air-cushion, measuring about 3 inches transversely and 2½ vertically. This cushion is placed against the aperture of the belly, and presses back the protrusion. The size of the pad varies with the size of the hernia, but it should always largely exceed the extent of the gap in the abdominal wall. The pad, when the apparatus is used for an infant, should not be too prominent, as it is then more difficult to keep in place, and also by pressing into the aperture hinders it from closing. The pad for an infant is best made of a disc of ivory, 1½ inch broad and ½ an inch to 1 inch thick, stitched in a little case in the centre of the girdle. The quantity of elastic tissue should be much less in the infant’s belt than in those for adults that the belt may be frequently washed. The difficulty of keeping the belt in place is obviated by attaching two bands to the upper border, to pass over the shoulders and cross behind before fastening to the belt, like braces. Two similar ones may be fastened to the lower border and carried under the thighs. These bands should be of soft webbing, and several pairs kept in store, that they may be frequently changed and washed. =Cauteries.= _Cautery irons._—These are masses of iron of different shapes; some pointed, others rounded like buttons, &c., set in a stem a foot long, fixed in a thick wooden handle. They are heated in a charcoal brazier or common fire to bright redness if required to destroy deeply, but short of redness if intended only to scorch the surface. As these irons are inconvenient for many cases from their bulk, and yet soon lose their heat if made small, other cauteries have been devised to which the heat can be quickly renewed. [Illustration: Fig. 112.—Gas cautery for large surfaces.]