Inflammations of bone are sometimes distinguished according as they affect the periosteum (Periostitis), the bone proper (Ostitis), or the bone-marrow (Osteomyelitis). Such a distinction, however, is not consistent with actual fact. We have already seen that in the growing bone the proper tela ossea is enveloped in an active cellular tissue, which is beneath the periosteum, in the substance of the bone filling its spaces, and in the medulla. In the adult the remains of this tissue is still present and capable of activity. In inflammations it is this tissue, which by some writers is altogether included as the bone-marrow, that is specially affected. The majority of cases of inflammation of bone occur in childhood, when this tissue is still active, and when inflammation occurs in adults the state of activity is restored. While this is true it will be understood that the phenomena of inflammation are frequently most manifest on the surface or in the marrow of bones, because the soft tissue is most abundant there. It is also to be remembered that the surface of bones is most exposed to injury, and that inflammations may thus arise which will chiefly affect the periosteum and superficial layers of the bone.