that portion of the wall adjoining the corn is struck. Finally,
exploration with the knife reveals the serious extent to which the injury
has developed. In a neglected case of this description it is even possible
to detect the presence of pus by the amount of swelling and fluctuating
condition of the coronet. The suppurative process has advanced in the
direction of least resistance, and is on the point of breaking through the
tissues immediately above the horn.

Lameness due to corn is oftentimes intermittent. With a simple corn, dry or
moist, this intermission is largely dependent on the degree of dryness of
the hoof or the road, and also on the character of the road surface. With a
neglected, suppurating corn, on the other hand, variation in the degree
of lameness, in addition to depending on circumstances such as these,
is dependent to a larger extent upon the changes occurring with the
suppuration. In this case the time of greatest lameness is immediately
before the pus gains outlet. Immediately after its exit at the coronet the
animal will go almost sound. Soundness continues so long as the opening at
the coronet remains clear. The tendency, however, is for the opening thus
made to quickly close again. Pus again accumulates, lameness arises as
before, and disappears again with the second discharge of the contents of
the sinus now formed.

_Pathological Anatomy_.--When dealing with their classification we gave in
outline the main pathological changes to be met with in corns. It now only
remains to give the same matter in slightly greater detail.

_In dry corn_ the changes we meet with are those accompanying blood
extravasation. From excessive compression of the parts, or from the effects
of direct injury, a portion of the sensitive sole has become lacerated.
The escaping blood stains the surrounding soft tissues after the manner
of blood extravasation elsewhere. If the escape of blood is sufficiently
large, the horn fibres in the immediate vicinity also are stained. It is
this stain in the horn that is the direct evidence of the injury, and is
itself popularly known as the corn. It may vary in size from quite a small
spot to a broad patch as large as half a crown, while its colour may be a
uniform red, or a mottled red and white. The microscopic changes in this
connection are illustrated in Fig. 99.

[Illustration: FIG. 99.--HORIZONTAL SECTION OF A CORN. The section cut at
about the base of the papillae of the sen