No person shall be retired, as provided in Section 4.28.090 and 4.28.100, or receive any benefit under said sections, unless there shall be filed with the board certificates of their disability, which certificates shall be subscribed and sworn to by two regularly licensed and practicing physicians. The board may require other evidence of disability before ordering such retirement and payment as aforesaid. (Ord. 3558-NS § 11, 1957)