Section 19. Any person having knowledge or possession of facts that tend to establish the guilt of any other person or corporation charged with bribery or illegal rebating, shall not be excused from giving testimony or producing evidence, when legally called upon to do so, on the ground that it may tend to incriminate him under the laws of the state; but no person shall be prosecuted or subject to any penalty or forfeiture for, or on account of, any transaction, matter, or thing concerning which he may so testify or produce evidence.