Professor Russell's superb monograph takes as its point of view that "the common background of hydrocephalus is formed by the single factor of obstruction, and the immense variety of pathological lesions productive of hydrocephalus have this single feature in common: all create an obstruction at some point in the pathway of the cerebrospinal fluid." In each instance of a large series of cases, Russell has been able to identify the cause of the obstruction, a record hardly approached in most neuropathologic laboratories.