A solution of the problem of the interrelationship of the known diseases of the central nervous system has been offered by various classifications. Spielmeyer,1 however, commented on the difficulty of such classifications since variable changes are produced by the same irritant and similar changes are found in totally different diseases. The glial foci of simple septic endocarditis are present also in typhus fever and reach their maximum in postvaccinal encephalitis. Mesodermal intra-adventitial infiltrations are characteristic of such dissimilar diseases as diffuse dementia paralytica and epidemic encephalitis with its marked predilection for areas of inflammation. Although poliomyelitis and epidemic encephalitis affect for the most part the same regions with similar inflammatory changes, the early leukocytic infiltration of poliomyelitis and the involvement of the motor cortex are lacking in epidemic encephalitis. Dementia paralytica and multiple sclerosis show similar areas of demyelinization which are, however, not related to the so-called demyelinization of