The _rapidity of growth_ of the wall varies, amounting in a month to from one-sixth to one-half of an inch. The average monthly growth in both shod and unshod horses of both sexes is, according to my own experiments, one-third of an inch. Hind hoofs grow faster than front hoofs, and unshod faster than shod. The hoofs of stallions grow more slowly than those of mares and geldings. Abundant =exercise=, proper grooming (flexibility and moistness of the horn), regular dressing of the wall, and =running barefoot= from time to time =favor growth=; while little or no exercise, dryness, and excessive length of the hoof hinder growth. The time required for the horn to grow from the coronet to the ground is, therefore, equally variable, and is, moreover, dependent upon the height (length of toe) of the hoof. At the toe the horn grows down in from eleven to thirteen months, at the mammæ or sides in from six to eight months, and at the quarters in from three to five months. The time required for the renewal of the entire hoof we term the _period of hoof renewal_. If, for example, we know exactly the rapidity of horn growth in a given case, we can estimate without difficulty the length of the “period of hoof renewal,” as well for the entire hoof as for each individual section of the wall. The duration of many diseases of the hoof (cracks, clefts, partial bendings of the wall, contractions, etc.) can be foretold with relative certainty only by knowing the period of hoof renewal. _Irregular growth_ sometimes takes place. The chief cause of this is usually an improper distribution of the body-weight over the hoof,—that is, an unbalanced foot. Wry hoofs of faulty positions of the limbs are often exposed to this evil; a faulty preparation of the hoof (dressing) for the shoe, as well as neglect of the colt’s hoofs, is in the majority of cases directly responsible for this condition.