§ 378. Washrooms. Every mercantile establishment, every restaurant, every office of a telegraph or messenger company in a city and every station, terminal or car barn where women employees of a street, surface, electric, subway or elevated railroad report for duty shall provide and maintain for employees adequate and convenient washrooms or washing facilities, separate for each sex wherever required by the rules of the board. Every washroom shall be adequately ventilated and heated and shall be lighted by artificial means where necessary.