In inflammation of bones and joints, only two of the osseous tissues are active: the marrow and the synovial membrane; that the ligaments, the cartilage, the bone tissue itself and probably the fibrous periosteum all take a purely passive part. This theory, as the author admits, is by no means generally accepted. In fact, by far the weight of opinion lies on the other side, most writers believing that the bone tissue itself is capable of active inflammation. The author considers the marrow, especially the lymphoid marrow, the constituent vulnerable to infection, and that its location determines the site of the localization of infection. In infancy practically all marrow is lymphoid; in childhood the lymphoid marrow gradually disappears from the shafts, and then slowly, with the lapse of years, from the ends of the bones also. The adult has little