At this stage the method of percussion recommends itself, and in many cases no more useful diagnostic agent is to be found than the ordinary hammer. As a preliminary, the foot of the sound limb should be always tapped first. This precaution will serve to bring to light what is frequently met with--the aversion nervous animals sometimes exhibit to this manner of manipulation of the hoof. Unless this is done, the ordinary objection to interference is apt to be read as evidence of pain. No aversion to the method being shown, the suspected foot is gently tapped in various places round the wall, a keen look-out being kept for any manifestation of tenderness. This may vary from a slight resentment to each tap, indicated by a sudden lifting and setting down again of the foot, to a complete removal of the foot from the ground, and a characteristic pawing of the air that points out clearly enough the seat of pain. Evidence of pain once given, the tapping is persisted in until, in some cases, the exact position of the tender spot is definitely located. Failing evidence obtained from percussion, attention should next be given to the shoeing. We may add here that, even when difficulties have to be encountered in doing it, it is always a wise plan to have the shoe removed. The nails should be removed one by one, the course they have taken, their point of emergence on the wall, and the condition of their broken ends all being carefully noted as they are withdrawn. The removed shoe should next be examined as to the coarseness or fineness of its punching and the 'pitch' of its nail-holes, and close attention given to the shape of its bearing surface. From that we may pass to a consideration of the underneath surface of the foot. The drawing-knife should be run lightly over the whole of its surface, the first thing to be noticed being the point of entrance of the nails as compared with the coarseness or fineness of the punching, and the staining or otherwise of the horn immediately around. We may thus be guided towards mischief arising from tight nailing apart from actual prick of the foot. This done, more than usual care should be taken in following up any other small prick or dark spot that may show itself upon the white surface of the cleaned sole. In any case, a suspicious-looking speck should be followed up with the searcher until it is either cut out or is traced to the sensitive structures. While this is done, we should also have noticed the condition of the horn at the seat of corn; should have noticed the shape of the heels, contracted or otherwise; and the appearance of the frog, clean or discharging.