The diagnosis of organic nervous diseases rests on a foundation built largely by anatomists, pathologists and physiologists. For this reason, it compares favorably in accuracy with diagnoses in other fields of medicine. In the localization of tumor of the brain, however, astonishing difficulties are often encountered. Thus, Magnan1 (1878) reported a case of tumor and softening in the region of the left rolandic fissure, in which there were convulsive movements on the left side. The patient also had dementia paralytica and the marked meningo-encephalitis on the right side explained the convulsions on the left. Tucker2 (1917) reported a case (case 4) of tumor of the left temporal lobe in which left hemiplegia was also present. Massive hemorrhage was noted in the right subcortical area. Meyer3 (1920) reported a case in which a supratentorial tumor had produced such marked herniation that the tentorial edge impinged on the right