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.

A point to be remembered in making this exploratory paring of the foot is the peculiar consistency of the horn of the frog, and its tendency to hide the existence of punctures.  In like manner, as a pin pierces a piece of indiarubber, and leaves no clearly visible trace of the hole it has made, so does a nail or other sharp object penetrate the frog, leaving but little to show for the mischief that has been done.

After all, even though we may have fully decided the foot is at fault, our case of lameness may remain obscure so far as a cause is concerned.  Nothing remains, then, but to acknowledge the inability to discover it, to advocate poulticing, or some other expectant palliative measure, and to bring the case up for further examination at no distant date.  Where, though we may have suspected the foot, we have not been able to definitely assure ourselves that there the mischief is to be found, a further method of examination presents itself—­namely, subcutaneous injections of cocaine along the course of the plantar nerves.

The salt of cocaine used is the hydrochlorate, 2-1/2 grains for a pony, 4 grains for a medium-sized animal, and 6 grains for a large horse.  A solution of this is made in boiled water (about 3 drams), and injected at the seat of the lower operation of neurectomy.

It is advisable to first render aseptic the seat of operation, and to sterilize both the needle and the syringe by boiling.  A suitable point to choose for the injection is exactly over the upper border of the lateral faces of the two sesamoids, the needle being introduced behind the cord formed by the nerve and accompanying vessels, and parallel with it.

It is possible that the vein or the artery may be wounded, but such accident is of little importance.  All that is necessary in that case is to partly withdraw the needle and again insert it.  It is advisable to use a twitch.

When the needle is in position, the injection should be made slowly, and at the same time the point of the needle should be made to describe a semicircular sweep, so as to spread the solution over as wide an area as is possible.