Complex sentence: Flournoy was a contemporary of Freud and his work influenced C. G. Jung's study of another medium, his cousin Héléne Preiswerk, which turned into Jung's doctoral dissertation in 1902.
Split into simpler sentences: Flournoy was a contemporary of Freud and his work influenced C. G. Jung's study of another medium, his cousin Héléne Preiswerk. This turned into Jung's doctoral dissertation in 1902.