Section 41. No person shall be excused from testifying or producing any papers in any inquest proceedings under sections thirty-five to forty, inclusive, on the ground that his testimony may tend to criminate him or subject him to a penalty or forfeiture, but he shall not be prosecuted or be subjected to a penalty or forfeiture for or on account of any action, matter or thing concerning which he may be required so to testify, except for perjury committed in such testimony.