Microscopic examination of the structures involved in such a case reveals the fact that with the contraction is an alteration in the normal direction of the horny and sensitive laminae.

They become bent backward, and, instead of the regular and normal arrangement depicted in Fig. 32, show the distorted appearance given in Fig. 101.

From the appearances and characters of the blood-stain in the horny sole we are able to deduce evidence relative to the duration and nature of the injury.

[ILLUSTRATION:  FIG. 101.—­PERPENDICULAR SECTION OF THE WALL OF A CONTRACTED QUARTER IN A CASE OF CHRONIC CORN.  Both the sensitive and horny laminae are bent backwards, and haemorrhages have taken place at the base of the sensitive laminae.]

When, for instance, the stain is not to be found in the superficial layers of the sole, but is only discoverable by deep paring, then the injury is a recent one.

Where the stain is met with in the superficial layers of horn, and is quickly pared out, then the injury has been inflicted some time before, and has not been repeated.  When, as is sometimes the case, layers of horn that are stained are found alternated with layers that are healthy, then we have evidence that the cause of the corn, whatever it may be, is not in constant operation.

Similar indication of the age of the injury is also afforded by the colour of the lesion.

A stain that is deep red is proof that the injury is comparatively recent.

A distinct yellow or greenish tinge, on the other hand, is evidence that the injury is an old one.

In the Moist Corn we have, in addition to the blood extravasation, the outpouring of the inflammatory exudate.  In the most superficial layer of the horn this may not be noticeable.  As one cuts deeper into the sole with the knife, however, it will be found that the lower layers of horn are more or less infiltrated with the discharge.  This gives to the horn a soft consistence, a yellow appearance, and a touch that is moist to the fingers.

With the accompanying inflammation the cells in the neighbourhood of the injury are enfeebled and their normal functions interfered with.  We may thus expect a corresponding interference with the growth of horn.  This is exactly what happens, and as one cuts deeper still into the horn a point is finally reached when a well-marked cavity is encountered.  A pale yellow and usually watery exudate fills it.  This cavity points out the exact spot where the force of the injury has been greatest, where death of certain cells of the keratogenous membrane has resulted, and where the natural formation of horn has for a time been suspended.