There are two varieties of ulcers as properly understood, viz. the simple or common ulcer and the specific or infective. The former is due to some local derangement of nutrition, the consequence of impaired circulation or innervation of the parts. The latter results from the action of specific organisms which have gained access to the body. The non-infective ulcer assumes a variety of forms, of which the following are of special interest to the veterinarian and the horse-owner.

The Simple Ulcer is a sore in which the process of healing has been arrested and followed by a more or less rapid extension of the wound. A number of causes may be individually or collectively concerned in bringing about this retrograde action. Among them the chief are mechanical irritation, as the chafing of a collar or a saddle, or any other part of the harness; undue movement of the injured part, such as occurs when the wound is situated on the aspect of flexion or extension of a joint, or over the seat of much-used muscles. It may also be induced by pressure.

Ulcers of this kind are covered with yellowish-red granulations, which are usually flush with the margin of the skin, and the edges are but slightly if at all thickened.

When severely irritated, acute inflammation is excited in these ulcers, and the surrounding skin becomes thickened by serous infiltration; there is also great soreness, and a free discharge of pus from the surface. The edges of the wound now present a somewhat irregular and sloughy appearance.