Finally, it cannot be denied that the work the horse is put to is largely responsible for the causation of corn.  In country animals corns are comparatively rare, while in animals in town, almost constantly upon hard paving, they are common.  This seems to point strongly to the fact that concussion through constant work upon unyielding roads is a great factor in their production.

Symptoms.—­Unless the discoloration of the horn is accidentally discovered by the smith, the simple, dry corn may go undetected.  The disturbance excited by it is so small, and the pain occasioned so slight, that the patient may offer no indication of its existence.

Ordinarily, however, the first symptom is that of pain.  The animal goes feelingly with one or both feet, in some cases even showing decided lameness.  The lameness, however, is in no way diagnostic, and the lesion itself must be discovered before an exact opinion can be pronounced.

As an aside, it is well to observe in this connection that a negative opinion as to the existence of corn should never be given unless the superficial layers of horn have first been removed with the knife.

When standing at rest the animal exhibits signs more or less common to all foot lamenesses.  He ‘points’ the foot—­in other words, the limb is slightly advanced, the fetlock partly flexed, and the heels from off the ground.  When both feet are affected they are pointed alternately, and the animal often manifests his uneasiness by repeated pawing movements, and by scraping his bedding behind him.

Should the injury run on to suppuration, the lameness becomes most acute.  The pawing movements become more pronounced, and there is evident disinclination on the part of the animal to place the foot squarely on the ground.  One is then led to manipulate the foot.  The hoof is hot to the touch.  Percussion causes the animal to flinch, and to flinch particularly when 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.