FAULTY CONFORMATION 121 
supply is lessened, their functions interfered with, and 
side-bones result. 
Causes.—Upon the causation of contraction a very great 
deal has been written, both by early veterinarians and by 
those of the present day. Many and widely differing 
opinions have been advanced, but a careful résumé of only 
a few will lead one to certain fixed conclusions. 
We may consider the causes of contraction under two 
headings—predisposing and exciting. 
Predisposing Causes of Contraction.—Among these we will 
first mention heredity, although it is possible it should not 
be deemed of so great account as it is by some. That the 
shape of certain feet, especially those with low heels and 
abnormally sloping walls, predisposes to contraction no one 
will deny. So long, however, as the animal goes unshod, 
so long does the foot maintain a normal condition of the 
heels. In other words, it is not until the tendency to con- 
traction already there is aggravated by careless shoeing and 
the effects of work that it operates to any noticeable extent. 
The degree of contraction wili also be very largely 
governed by the amount of the development of the frog. 
With a frog of good size, low down, and taking part in the 
pressure of the foot on the ground, contraction will be pre- 
vented. On the other hand, an ill-developed frog, one 
wasted by long-continued and spreading thrush, or one 
robbed of its normal function by excessive paring in the 
forge, is a common starting-point of the condition we are 
considering. We have already referred to this in 
Chapter ITI., when considering the experiments of Lungwitz 
in this connection. What we have to bear in mind in these 
experiments is that the application of a pad to the frog, in 
such a manner that effective ground-pressure is obtained, 
results always in a marked expansion of the heels, and 
that, with counter-pressure with the ground absent, ex- 
pansion occurs to little or no extent. This is proof positive 
of the enormous part the frog plays in maintaining an open 
and elastic condition of the heels—a fact so insisted on by 
Coleman. 
