The inflammatory irritation excites proliferating and degenerating processes in the cells and basis-substance of the cartilage covering the bones, and the changes described in connection with acute rheumatic arthritis ensue. Those parts of the cartilage covering the bones which suffer pressure in locomotion fibrillate on their surface, and either undergo mucous degeneration, resulting in ulceration and complete absorption, or are thinned and worn away by attrition. In either way the ends of the bones become laid bare. Those portions of the cartilage at the periphery of the joints which escape compression in the erect posture likewise proliferate, but, according to Cornil and Ranvier, in consequence of being covered by the synovial membrane the proliferating elements are retained in situ, instead of escaping into the articular cavity, and develop into actual cartilage, and may ultimately ossify. In this way irregular masses of cartilage (enchondromata) and bone (osteophytes) form around the heads of the bones, enlarging them considerably, altering their shape, encroaching upon the articular cavity as well as extending up the shafts of the bones, and displacing the capsules of the articulations. Similar productions of cartilage sometimes form in the thickened capsules and ligaments, especially in very protracted cases, or these parts become infiltrated with lime salts. While these processes are going on at the periphery and the centre of the cartilages, in its deeper layers the proliferating cells are undergoing ossification and rendering the ends of the bones very dense and compact, so that under the attrition to which they are exposed by the articular movements they acquire the smoothness, polish, and white aspect of ivory (eburnated). It is probable that the articular ends of the bones participate in this proliferation and development of bone, which increases their compactness and is followed by eburnation. That the bone itself does sometimes play a part in the hyperostosis which is in progress is shown by an increase of an inch in the length of the right ramus of the maxilla over that of the left in Adams's first plate.[228] Forster's[229] and Ziegler's[230] later investigations confirm this view. Nor is the periosteum exempted from the proliferating process which may have long existed in the several articular tissues, as is shown by the considerable enlargement of the diameter of the shaft of the long bones and by the osteophytes which form on the exterior of the vertebræ and often unite several of them together by a series of osseous splints, interfering with the mobility of the spine. Notwithstanding this development of cartilage and bone upon the exterior of the articular extremities, the interior, especially in old people or in very chronic examples of the general form of the disease, or rarely in the partial form, undergoes degeneration and atrophy. The spongy substance becomes rarefied,