It is claimed that Parisian masochists didn't merely volunteer for treatment in the Dungeon scenes, but actually paid for the privilege.
The film was refused a certificate in the U.K. due to the reason that "Such material in the public cinema might stimulate imitative experimentation "
(BBFC head censor James Ferman)
This film is part of the Criterion Collection, spine #223.
Extensively commented and illustrated in "Le Masochisme au Cinéma", by Jean Streff. Editions Veyrier. Paris: 1978. Pages 48-51.
Title translation: Mistress.