In the second case the shoe is what is termed 'set' at the heel. Here it is the plane of the _wearing_ surface of the shoe that is altered. The hinder portion of the required heel is thinned so that its lower surface does not come into contact with the ground. By this means the wall is freed from concussion and pressure. At the same time the upper surface of the shoe is in contact with the wall of the foot (see Fig. 105). This 'setting' of the shoe is preferable to the method first described. It affords a greater protection to the foot, and does not allow of fragments of stone and flint getting in between the foot and the shoe, and so giving rise to further mischief. The 'set' portion should be fitted full and long. It is obvious, too, that the animal should not be allowed to carry the shoe too long; otherwise, as the other portion of the shoe wears down to the level of the 'set' heel, pressure on the tender part of the foot will again result. [Illustration: FIG. 104.--SHOE WITH A 'DROPPED' HEEL.] [Illustration: FIG. 105.--SHOE WITH A 'SET' HEEL.] In applying surgical shoes for corn of long standing, it must be remembered that the protection so afforded must be continued for some time. It is not sufficient to see the lesion itself disappear. In addition to that there is also, in the majority of cases, a certain amount of contraction to be overcome. This can only be done by continuing the use of a leather sole or some form of frog or bar-pad as recommended for the relief of that condition. C. CHRONIC BRUISED SOLE. A similar condition to that of corn may be met with in other positions on the sole. It is described by Rogerson as sand-crack of the sole[A], and is invariably met with around that portion of the sole in contact with the shoe. [Footnote A: _Veterinarian_, vol. lxiii., p. 51.] The animal is lame, and the shoe is removed in order to ascertain the cause. Nothing at first is noticeable except that the animal flinches when pressure is applied to the spot with the pincers, or the sole is tapped with the hammer. On removing the sole with the knife, however, a distinct black mark is discovered, which, when followed up by careful paring, is often found to have pus at the bottom. In this case the injury has resulted, as we have already intimated elsewhere, from causing the animal to wear for too long a time a shoe with too broad a web or insufficiently seated. Or it may have originated with the irritation set up by foreign and hard substances between the web of the shoe and the foot. In his description of this condition Mr. Rogerson draws attention to the fact that the pus found should not be wrongly attributed to accidental pricking of the foot. He says: