The problems concerning the causation and the distinctive morphologic features of the several forms of nonsuppurative disease of the central nervous system, though recently subjected to searching investigations, are still awaiting solution. The efforts in this direction continue to be blocked, primarily by the failure to find the causative agent of the disease in question, and are in large measure retarded by the lack of full agreement among morphologists in the interpretation of the basic phenomena that underly the conception of inflammation. It is obvious that terms such as encephalitis, encephalomyelitis and similar designations, adapted for inflammatory diseases in the various subdivisions of the central nervous system, are of doubtful service without a precise knowledge of what constitutes inflammation. They will remain so, unless the morphologic symptom complex of the so-called inflammatory disease of the central nervous system is clearly defined. The conflicting views held by various schools, led by