122 DISEASES OF THE HORSE’S FOOT 
It is worthy of mention, 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 in- 
tensity in the hot, dry months of summer, than in the 
