Proof of duty, occupational disease, or ordinary disability shall be furnished to the Board by at least one licensed and practicing physician appointed by the Board. In cases where the Board requires the applicant to obtain a second opinion, the applicant may select a physician from a list of qualified licensed and practicing physicians which shall be established and maintained by the board. The Board may require other evidence of disability. A disabled fireman who is receiving a duty, occupational disease, or ordinary disability benefit shall be examined at least once a year or such longer period as determined by the Board, by one or more licensed and practicing physicians appointed by the board; however such examination may be waived by the Board if the appointed physician certifies in writing to the Board that the disability of the fireman is of such a nature as to render him permanently disabled and unable ever to return to service.
     When the disability ceases, the Board shall discontinue payment of the benefit and the fireman shall be returned to service in his proper rank or grade.