PURULENT PERIOSTITIS follows wounds which reach the periosteum and become infected, as observed in compound fractures, or it may result from advancing purulent conditions in neighboring structures, as in foul foot. It may also occur in the course of an infectious disease, when small abscesses are formed under the periosteum (subperiosteal abscess). It may lead to necrosis of the bone or a fistulous tract from the bone to the surface. There is usually much pain and fever, and the odor from the wound is offensive. _Treatment._--In this form of periostitis the periosteum should be freely incised, followed either by continuous irrigation or frequent injection of the wound with antiseptic solutions. FIBROUS PERIOSTITIS.--This form of the disease consists in the thickening of the outer layer of the periosteum from the inflammation reaching it from neighboring structures. This newly formed fibrous tissue may become ossified or may transmit the inflammation to the deeper bony structures. It is frequently seen in cases in which there has been an intense inflammation of the skin close to an underlying bone. _Treatment._--The treatment should be the same as that recommended for aseptic periostitis. OSTEOMYELITIS. This term refers to an inflammation of the bone marrow, which is most commonly seen following the bacterial infection of a compound fracture and usually results in pus formation. The bone is melted away and pus escapes from the bone under the periosteum, involving the soft tissues. It is principally confined to the long bones and seldom affects more than one. _Treatment._--The bone should be opened for the purpose of curetting out the diseased portion of the marrow cavity and removing all the necrotic pieces of bone. This should be undertaken only by a competent veterinarian. The after-treatment consists in tamponing the wound with pledgets of iodoform gauze or a mixture of iodoform 1 part and glycerin 4 parts. The wound in the soft tissue should be kept open until the cavity in the bone has filled with granulation tissue. RICKETS.