The mercury rubber applied an ointment containing mercury to the bather as directed by their physician to treat syphilis. It was applied using a glove or brush. Mercury was the primary treatment for syphilis from the 1500s until the advent of penicillin in the 1940s. Before the park hired a medical director to supervise bathhouse operations, bath attendants were required to rub the mercury and to supply the necessary ointment.
After 1910, regulations specified that attendants not be required to rub mercury or supply the ointment. A male and a female mercury rubber were on staff, however, generally in combination with another duty.
