however, that loss of the frog's function does not
operate to nearly so serious an extent in horses with high, upright heels
as in those with the heels low and excessively sloping.

In illustrating this, Mr. Dollar, in his work on shoeing, mentions the case
of a pair of trotting horses of similar age, size, and weight, each having
weak fore-heels. In one case the hoofs were flat, in the other upright. The
horse with the flat hoofs suffered from contraction, while the other did
not.

The reason appears to be that in the animal with upright hoofs the
proportion of body-weight borne by the heels is considerably less than in
those with the hoofs flat and sloping.

Certain conditions of the horn-producing membranes also predispose to
contraction. For example, in horses reared on marshy soils, and afterwards
transferred to standing in town stables, we find that a dry and brittle
condition of the horn supervenes. This we may regard as a low form of
laminitis, brought about by the heat of the material upon which the animal
is standing, and the congestion of the feet engendered by his enforced
standing for long periods in one position, as opposed to the more or less
continuous exercise when at pasture. With the hoof in this condition it
loses by evaporation the moisture that normally it should contain, and, as
we might expect, a certain degree of contraction of its structure is the
inevitable result.

We thus see that contraction brought about in this way is not so much
caused by the heat of the stable, as it is by the decreased ability of the
horn to retain its own moisture.

On the other hand, it cannot be denied that excessive warmth and dryness
combined tend also to an undue abstraction of moisture, even from the horn
of the healthy foot; and this explains in great measure how it is that
lameness, as a rule, and especially that proceeding from contracted heels,
is far more frequent and of greater intensity in the hot, dry months of
summer, than in the cooler and more humid atmosphere of winter. It is
interesting to note, too, that an alternation of humidity and dryness
is far more liable to injure the quality of the horn and tend to its
contraction than the long-continued effects of dryness alone. A common
illustration of this is to be found in the effects of the ordinary
poultice. Everyone knows that when, after a few days' application, they are
discontinued, we get as a result an abnormally dry and brittle state of
th