(a) Blistering the Coronet.—­In a simple case, where the crack is superficial and close under the coronary margin of the wall, a sharp cantharides blister to the coronet immediately above it will have the desired effect.  An increased secretion of horn is brought about, and by this simple means the crack prevented from becoming longer.  Very often this is all that is necessary.  In fact, we may say here that, no matter what other treatment is adopted, the simultaneous application of a blister to the coronet is always beneficial.  To derive full advantages therefrom, the blistering should be repeated several times at intervals of about a fortnight.

(b) Clamping the Crack.—­When the services of a skilled smith are at hand, one of the readiest methods of performing this is to draw the edges of the crack together with an ordinary horse-nail.

On each side of the crack a small horizontal furrow is burned or cut into the wall, leaving the horn for about 1/4 inch on each side of the crack intact.  This provides a groove for the ends of the clamping-nail to rest in, and brings them flush with the outer surface of the wall.  The nail is then driven carefully home through the crack, and the pointed end grasped by the farrier’s pincers.  The edges of the crack are then drawn tightly together, and the nail firmly clenched.

[Illustration:  FIG. 86.—­THE SAND-CRACK FIRING-IRON.]

’The horse-nails are prepared in the ordinary way as for driving, with the exception that each is pointed on the reverse side, to prevent puncturing the sensitive structures.  Before being used the nails are put in a vice, and the head hammered to form a shoulder, to prevent their being driven too far into the wall, and breaking out the hold.’[A]

[Footnote A:  Veterinarian, vol. xlviii., p. 100.]

Before driving the nail some operators burn or bore a hole for it.  Opinion seems to differ as to whether this is at all necessary.

A method of clamping which, on account of its simplicity, has become greatly popular, is that of Vachette.  For this operation is needed the outfit depicted in Figs. 86 and 87.

[Illustration:  FIG. 87.—­THE SAND-CRACK FORCEPS AND CLAMP.]

With the special firing-iron (Fig. 86) an indentation, sufficiently large to admit the points of the clamp (Fig. 87), is made on each side of the crack.  The clamp is then adjusted, and pressed home tight by means of the sand-crack forceps (Fig. 87).  According to the length of the crack, one, two, or three clamps may be necessary.  Another useful clamp, though far more complicated in its structure, is that of Professor McGill (Fig. 88).

[Illustration:  FIG. 88.—­MCGILL’s SAND-CRACK CLAMP.]

’The object of this invention is to arrange on a spindle, which is screw-threaded at one end with a right-hand thread and at the other with a left-hand thread, two clips or clamps, free to travel on the thread, there being a nut between the two which can be turned by a spanner.  The clips are placed on the hoof, one on each side of the sand-crack, the hoof being prepared to receive the instrument by filing a groove or notch for the clamps to fit into, and by turning the nut on the screw the clamps are brought towards each other, and the crack thus prevented from spreading.’[A]