The term "spasticity" in this report is used to describe the clinical picture produced by extensive lesions mainly of the corticospinal motor systems, and in some instances presumably also of other motor systems, subcortical in origin. "Spasticity" thus has to be distinguished from "rigidity," which in association with tremor, or occasionally without it, is seen (among other phenomena) in Parkinson's disease, and also from "decerebrate rigidity." An attempt will be made later to clarify the interrelationships of these conditions, which have not been clearly distinguished by older neurologists.1
It has not been possible to include in this investigation the study of flaccid paralysis following lesions of the brain and long tracts. This syndrome, rarely seen as a permanent state in man, has not been observed in our series of cases. It has been studied in subhuman primates especially by Fulton and his co-workers,2 who ascribed the syndrome to