of the whole of the foot. Its
longitudinal and transverse diameters become enormously increased, and the
whole foot apparently flattened from above to below (see Fig. 136). This
indicates that not only has the horny sole been entirely destroyed, but
that the destructive process has also extended to the greater part of the
lower half of the wall, with a consequent hypertrophy of exposed soft
structures, and a sinking of the bony column, similar to that which occurs
in laminitis, but not so pronounced.

[Illustration: FIG. 136.--FOOT WITH ADVANCED CANKER.]

A further aspect of the badly-cankered foot is to be found in an apparently
enormous increase in the length of the wall. This we have seen protruding
for quite 5 inches beyond the plane of the sole. It simply indicates that,
in order to keep the animal at work, the smith has at every shoeing spared
the wall, so that the diseased structures might be kept from contact with
the ground.

As we have said before, pain and other symptoms of distress are quite
absent. Animals affected with canker for a long time maintain their
condition, feed well, and are quite capable of performing work under
ordinary conditions.

_Differential Diagnosis and Prognosis_.--Perhaps the only disease with
which canker may be confounded is thrush. They should, however, be easily
distinguishable. The discharge from thrush is not so profuse, and is
thicker and darker in colour, while the loosening of the horn is almost
entirely absent. Furthermore, thrush shows no tendency to spread, and, even
when left untreated, may remain confined to the frog for months, and even
years. Canker, on the other hand, is slowly progressive, and soon shows the
characteristic fungoid excresences, which growths are in thrush never seen.
A further point of difference is discovered when treatment is commenced.
Canker is found to be refractory to a point that is absolutely
disheartening, while thrush, with careful attention, is soon got under
hand, and a permanent cure effected.

The prognosis must be guarded. By many canker has been said to be
incurable. This, however, has been clearly shown to be wrong. When the
animal is young, and treatment may reasonably be judged to be economical,
then a favourable prognosis may be indulged in, provided the veterinary
surgeon intends to put into that treatment a more than ordinary amount of
individual care and attendance. Even then, however, he will have to be very
largely guide