No person shall be excused from attending and testifying, or from producing books and papers before the commission, or in obedience to the subpoena of the commission, whether such subpoena is issued or signed by one or more of the members of the commission, in any investigation held by or before the commission, or in any civil action or proceeding in any court by or against the commission, provided for in this title, on the ground or for the reason that the testimony or evidence, documentary or otherwise, required of him may tend to incriminate him or subject him to penalty or forfeiture. But no person shall be prosecuted or subjected to any penalty or forfeiture for or on account of any transaction, matter or thing concerning which he may be required to testify or produce evidence, documentary or otherwise before said commission, or in obedience to its subpoena, or in any such action or proceeding. No person testifying shall be exempted from prosecution and punishment for perjury committed in so testifying.