A corn is really a bruise of the lining membrane covering the bones of the foot, immediately beneath the horny sole, and may occur at any part of this; though it is most frequently observed at the inside heel, in the angle between the frog and the bar, where the sole is thinnest and the pressure is greatest. It is manifested by the blood-stained horn, which is sometimes quite soft and spongy, and increasing in this, on being pared down to the sensitive part. In other cases the stain is yellow and red; and in other cases, again, it is quite superficial, and can be removed. Certain kinds of feet are more predisposed to corns than others, those with weak heels, or very strong ones, being most liable. The kind of work has also something to do with their production, fast pace and hard roads very often causing them; but perhaps the most frequent cause is paring and rasping in shoeing, and faulty shape, or bad application, of the shoe, or allowing the shoe to remain too long on. In slight cases lameness may not be present, and even apparently bad corns do not always produce lameness.
If there is pain when the horse is standing, he usually "points" the foot; and a tap with a hammer on the wall adjoining the seat of the corn will make him wince or exhibit uneasiness.
The prevention of corns largely depends upon a proper method of shoeing; this has already been touched upon. If there is a natural tendency to them, the horse should either be shod with periplantar shoes, with tips, or with three-quarter shoes. In all cases the frog should be allowed to come on the ground, if possible. If there is lameness, the shoe should be removed, and the seat of corn pared out to ascertain the amount of damage; and if there be matter, to allow it to escape. Afterwards foment and poultice until the pain and lameness have disappeared; then apply a shoe which will not press upon the heel, the kind of shoe depending upon the extent of the injury and the structure of the foot. The danger from a suppurating corn is in the matter burrowing its way up to the coronet and forming a "quittor."