_Treatment._—It aims to remove the lameness and to favor growth of coherent horn. In the first place the removal of the exciting causes, followed by proper shortening of the wall. We should apply a shoe whose bearing-surface _inclines slightly downward and inward_, is perfectly smooth, and wide enough to cover the wall, white line, and outer border of the sole; the iron should be only moderately warm. Where there is lameness we use a leather sole with packing, or a =bar-shoe=. The loose wall should be freed from shoe-pressure only when it does not extend far along the white line. When the separation is extensive the loose wall should not be lowered. The crack should be filled with wood-tar, crude turpentine, or soft grafting-wax. If a loose wall occur upon the foot of a horse while running barefoot, all separated horn should be removed; if, on account of the nature of the ground, this seems to be impracticable, the hoof must be shod. _Care of the Hoof._—Shoe at least every four to five weeks. Preserve the pliancy and toughness of the horn by judicious moistening. 4. HOLLOW WALL. A _hollow wall is one in which a separation has occurred between the middle layer of the wall and the keraphyllous layer_. This crack or separation always extends in the direction of the layers of the wall (Fig. 223, _b_). [Illustration: FIG. 223. An imaginary transverse vertical section of a hoof showing (_a_) loose wall and (_b_) hollow wall.] _Occurrence._—Quite rare. We should suspect a hollow wall when a part of the wall _rounds out prominently beyond the rest_, and gives forth a hollow (resonant) sound when struck. The white line presents a crack, yet we should hesitate to form a conclusion as to the extent of the separation from the extent of the crack along the white line, since the latter may be considerably smaller. The separation extends higher up the wall than in the case of loose wall, frequently to the coronet. The cavity is usually filled with crumbling, disintegrated horn. Hollow wall is not often accompanied by pain. Lameness may arise, however, if the hollow section of wall assists in bearing the body-weight, and if the animal does fast work upon paved streets. _Causes._—Mechanical influences resulting in chronic inflammation of fleshy leaves. _Treatment._—A cure is possible, but requires considerable time. In shoeing, which should always aim to _relieve pressure_ from the hollow section of wall, we cleanse the cavity and fill it with oakum and tar, crude turpentine, or wax. Where the separation is very extensive we use a _bar-shoe_. The time required for complete cure of hollow and loose walls will depend upon the height of the separation (see growth of the hoof, page 82). 5. THRUSH OF THE FROG.