DISEASES OF THE LATERAL CARTILAGES 869 
lateral cartilage persisting as cartilage is due in large 
measure to its constant movement. Directly, therefore, 
it is placed in a state of comparative idleness, then it com- 
mences to ossify, more particularly if there should at the 
same time be a tendency to a low type of inflammation of 
the parts. 
Does this latter exist? We may safely say that it does. 
It is in this way: The secondary effect of loss of ground- 
pressure upon the frog and plantar cushion is to bring 
about contraction of the heels. With this we get compres- 
sion of the parts within, with a certain amount of irritation 
and the exact low type of inflammatory phenomena calcu- 
lated to assist in the bone-forming process. 
The fact that concussion acts as a cause explains in great 
measure how it is that side-bones are more frequent in cart 
animals than in nags, and also why they should be more 
common in the fore-feet than in the hind. Taking, in both 
animals, a rough calculation as to the weight of body 
carried by feet of a certain size, we notice at once that the 
cart animal has proportionately more weight to carry than 
has the nag. Concussion to the foot is therefore greater. 
The greater part of the body-weight is borne by the fore- 
limbs. Concussion is therefore greater to the fore-feet than 
to the hind. 
This, however, does not explain altogether the compara- 
tive immunity of the nag animal from this defect. He, too, 
must also be subject to the effects of concussion, especially 
when his higher and faster action is taken into account. 
To our minds there is only one explanation to be offered 
here. We point at once to the years of constant and 
judicious breeding of the nag. Compare that with the. 
relatively few minutes that have been devoted to a more 
careful selection of the cart animal, and we at once see a 
possible explanation. That the explanation holds some 
amount of truth is borne out by the fact that, since a greater 
attention has been paid to the selection of our cart animals, 
side-bone has grown a great deal less common. 
Is side-bone hereditary? We can best answer that by 
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