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 72 of elasticity, expansion, and contraction to obviate all danger from concussion.

As regards wear and tear there is nothing to fear; for, as ‘Kangaroo’ wrote in the ‘Field,’ ‘it is impossible for a horse to become footsore in the frog, sole, or heel of his foot, as a result of travelling barefoot.’ The horn of which the frog is formed differs from the horn of the sole in nature; and both of them are unlike the horn of the wall, of which latter the description by Mr. Douglas has already been given. The same authority says of the frog: ‘In structure the horn of the frog may be compared to horsehair in the compressed state as used for stuffing sofas;  and, if we can imagine this hair to be mixed with a fatty adhesive substance, we shall form a fair idea what the tough elastic frog resembles when under microscopic inspection.’ ‘The frog is only a continuation of the coronet;  and, from its wedge-like form, and nearly total insensibility to feeling, proves that it is meant to take a bearing upon the ground, where it is useful to the animal either in action or repose;  in the former it acts as a buffer, preventing concussion, whilst its hold upon the smoothest surfaces prevents slipping.’ Of the sole he says:  ‘Over its surface there is no glazy-gluey layer to preserve its moisture, as in the crust;  while its fibres, stretched like strings, layer over layer, are as unlike the woolly, oily, substance of the frog as the horn of the crust differs from the bones which it covers. In one respect the sole resembles the frog; which is, that the outer layer of fibres in