The author maintains that Hughlings Jackson has exerted a great influence in psychiatry. In the monograph, On Aphasia, which was translated into English by Stengel, Freud demonstrated a close familiarity with Jackson's writings, which contained such fundamental psychoanalytic concepts as regression, psychic determinism, psychodynamics, unconscious mental processes, and resistance. Stengel believes Freud's failure to acknowledge an indebtedness to Jackson might be explained by 'Freud's attitude to his prepsychoanalytic period, which he treated as a closed book'.