ent of navicular disease are an insufficient
plantar cushion, a small frog, high heels, excessive knee action, and
contracted heels. Finally, the environments of domestication and use,
such as dry stables, heavy pulling, bad shoeing, punctured wounds, etc.,
all have their influence in developing this disease.

_Symptoms._--In the early stages of navicular disease the symptoms are
generally very obscure. When the disease begins in inflammation of the
navicular bone, the animal while at rest points the affected foot a
time before any lameness is seen. While at work he apparently travels as
well as ever, but when placed in the stable one foot is set out in front
of the other, resting on the toe, with fetlock and knee flexed. After a
time, if the case is closely watched, the animal takes a few lame steps
while at work, but the lameness disappears as suddenly as it came, and
the driver doubts whether the animal was really lame at all. Later the
patient has a lame spell which may last during a greater part of the
day, but the next morning it is gone; he leaves the stable all right,
but goes lame again during the day. In times he has a severe attack of
lameness, which may last for a week or more, when a remission takes
place and it may be weeks or months before another attack supervenes.
Finally, he becomes constantly lame, and the more he is used the greater
the lameness.

In the lameness from navicular disease the affected leg always takes a
short step, and the toe of the foot first strikes the ground; so the
shoe is most worn at this point. If the patient is made to move
backward, the foot is set down with exceeding great care, and the weight
rests upon the affected leg but a moment. When exercised he often
stumbles, and if the road is rough he may fall on his knees. If he is
lame in both feet the gait is stilty, the shoulders seem stiff, and, if
made to work, he sweats profusely from intense pain. Early in the
development of the disease a careful examination will reveal some
increased heat in the heels and frog, particularly after work; as the
disease progresses this becomes more marked, until the whole foot is hot
to the touch. At the same time there is an increased sensibility of the
foot, for the patient flinches from the percussion of a hammer lightly
applied to the frog and heels or from the pressure of the smith's
pincers. The frog is generally shrunken, often of a pale-red color, and
at times is affected with thrus