Other and minor predisposing causes are those mainly referring to an unnatural dryness of the hoof when animals reared in the country are put to work in large towns. We here really get several predisposing causes combining. A sudden change is made from a more or less moist condition underfoot to one excessively dry. The character of the travelling is wholly altered from occasional work upon soft lands to continual labour upon hard-paved roads. The horn is often exposed to the vicious influences of unsuitable litter, the application of unsuitable dressings, and the deleterious effects of the street mud of our cities. All these play their part in determining a condition of the horn, rendering it open to receive the effects of the more exciting causes which we shall next consider. _Exciting Causes_.--Than the shoeing, no more frequent and exciting cause of corn exists. Whatever the predisposing influences may be, it is the shoeing that in nearly every case completes the list, and finally inflicts the injury. The evils in this connection we shall consider under two headings--viz., (1) the manner in which the foot is pared; (2) the make and fitting of the shoe. First among the faulty preparations of the foot comes that of excessive thinning of the sole, especially in the regions subject to corn. The farrier addicted to this is not as a rule content to confine his operations to the sole alone. In addition, the frog and the bars also suffer from the too lavish use of his knife. His main object is doubtless that of giving a broad and open appearance to the foot. It follows from this that his operations are confined more to the posterior than the anterior parts of the foot, and that the toe is therefore left too long. This gives us a combination of causes leading to pressure and bruises upon the sensitive structures at the seat of corn. By this unequal paring of the toe and the heels greater weight is thrown upon the posterior half of the foot. What then happens to the structures thinned as we have described is this: the pared frog, lessened in volume, does not meet the ground. It therefore fails to expand laterally with weight, and cannot assist, as normally it should, in aiding the heels generally in their movements of expansion. The weakened bars and the thinned sole, meeting with no opposition from the frog, give downwards and inwards with the body-weight at the precise moment these movements should be directed mainly outwards. As a further result of non-resistance on the part of the frog, this time in a lateral direction, the bars, the sole, and the wall at the heels all contract at the exact time they should expand. The end result must mean abnormal pressure and bruising of the sensitive structures in that particular region. Naturally, also, the excessive thinning of the horn renders direct injury to the sole from stones or other objects in the road far more probable.