Section 13
SEC. 13. In airy proceeding had before said Board or in any civil or criminal proceeding in any court in the Philippine Islands, growing out of any alleged violation of law or regulation under the provisions of this Act, concerning any public-service corporation, no person shall be excused from appearing and testifying as a witness or from producing before said Board, or any member thereof, or any court, any books, papers, tariffs, contracts, agreements, or other document or tilings called for by the Board, or any member thereof, or by any court, upon the ground or for the reason that the evidence, documentary or otherwise, required of him may tend to criminate him or subject him to a penalty or forfeiture; but no such person shall be prosecuted or .subjected to any penalty or forfeiture for or on account of any transaction, matter, or thing concerning which lie may testify or produce evidence, documentary or otherwise, before said Board or any member thereof, or any court: Provided, however, That no such person so testifying shall be exempt from prosecution or punishment for perjury committed in the course of any proceeding or investigation before such Board or any member thereof, or any court: And provided further, That such immunity shall extend only to a natural person who in obedience to a subpoena gives testimony under oath or produces evidence, documentary or otherwise, under oath.