Section 19. If the name of an accused person is unknown to the grand jury, he may be described by a fictitious name or by any other practicable description, with an allegation that his real name is unknown. An indictment of the defendant by a fictitious or erroneous name shall not be ground for abatement; but if at any subsequent stage of the proceedings his true name is discovered, it shall be entered on the record and may be used in the subsequent proceedings, with a reference to the fact that he was indicted by the name or description mentioned in the indictment.