It is generally accepted that focal and other infections are the cause of many cases of arthritis. It is the belief of some that all cases are due to this agency alone, but dispassionate students of the disease are almost unanimous in the belief that other factors also play a rôle, and that focal infection is often only the "match to the priming," even when operative. There is also strong evidence that focal infection may arise as the result, as well as the cause, of the arthritic syndrome. In any event, the manner in which bacteriologic infection exercises its influence has not been made clear. There are cases of arthritis undoubtedly characterized by bacteria in situ and even by the formation of free pus; but the evidence that all cases of arthritis are caused and perpetuated by bacteria in the joint tissues is far from convincing. The inclination to ascribe