"Farriery is the art of shoeing horses, and can only be properly learned by a long practical experience in the shoeing-forge.  If the foot of the horse were not a living object perhaps the training obtained in the forge would be all that was necessary for efficient workmanship.  As, however, the hoof is constantly growing, it is constantly changing in form.  The duty of a farrier therefore is not merely to fix a shoe upon the hoof but to reduce the hoof to proper proportions before doing so.  Now, as the hoof is only the outer covering of a complex and sensitive foot, damage to the exterior surface may injure the structures within.  Injury does frequently result, and not always from carelessness.  Perhaps as much injury follows careful work, based upon wrong principles, as slovenly work carried out in perfect ignorance of any principle.  The injury to feet resulting from shoeing may not be apparent at once.  It may be, and often is, of a slow and gradual nature, and not credited to its true cause until the horse is rendered an incurable cripple."