+Chronic Synovitis.+ While it is true that an inflammation of a synovial membrane cannot long remain without extending to the other joint structures, the fact remains that symptoms peculiar to synovitis often persist for months. These are properly viewed as constituting a condition of chronicity. The active swelling and abundant effusion, belonging to the acute stage, subside, but an undue amount of fluid remains, with some pain and weakness. If, with proper treatment and rest, these symptoms persist, there is an extension of the process to the bone ends and an exacerbation of symptoms. The subsidence of a chronic synovitis generally leaves a weak and impaired joint, though pain may be absent. Movements, especially in extension, are restricted, and grating or cracking remain as evidences of the roughened membrane. +Treatment.+ The mere presence of a superabundance of fluid in a joint does not in itself constitute a diseased state, but may be the evidence of impaired circulation of the part. Absorption may occur with rest and tight bandaging, or with massage, friction, and baking, results may often be obtained. Certain cases resisting such procedures are best treated with a plaster of Paris cast to immobilize the part for several months. When the affection is of long standing and the joint is much distended it may be termed _hydrops articuli_ or _hydrarthrosis_. When, in spite of all the methods of treatment here described, the condition does not yield, very good results may be obtained by the aspiration of the fluid, and the injection of a few drams of a three per cent. or five per cent. solution of carbolic acid. This operation, though simple, requires every aseptic precaution, and should never be performed in the presence of any acute symptoms. For other phases of Synovitis see Arthritis. +ARTHRITIS+ The structures of a joint are: bone, cartilage, ligaments, synovial membrane and, in some cases, fibrocartilage. Hence, a joint inflammation is an inflammation of all of these structures, and is designated, _arthritis_. The inflammation may begin in any one of these structures, but sooner or later, all are involved. The synovial membrane, however, when inflamed, seems to prove an exception to the rule in that inflammation may or may not extend from it to the rest of the joint. If such an extension does take place we have an arthritis. We may therefore have two distinct classes of joint inflammation: (1) the varieties of synovitis, and (2) the varieties of arthritis. These inflammations may be acute or chronic. In synovitis there is only the inflammation of the synovial membrane, while in arthritis there is inflammation of the synovial membrane plus inflammation of the bone covering (_periostitis_); of the bone (_osteitis_); of cartilage (_chondritis_); of bone marrow (_osteomyelitis_); and also a cellulitis of the ligaments attached to the joint involved.