After any member of the police force, fire department, or band has been retired upon pension by reason of disability, the board of trustees shall have the right at any time to cause the retired member again to be brought before it and examined by the medical board, and shall also have the right to examine other witnesses for the purpose of discovering whether the disability still continues, and whether the retired member should remain on the pension roll; but the retired member shall be retained on the pension roll until reinstated in the service of the police force, fire department or band, except in case of dismissal or resignation. The retired member shall be entitled to notice, and to be present at the hearing of evidence, shall be permitted to propound any question pertinent or relevant to the matter and shall also have the right to introduce evidence upon the retired member’s own behalf. All witnesses so produced shall be examined under oath and any member of the board of trustees is authorized to administer the oath. Should the retired member recover from the retired member’s disability and be, in the opinion of the medical board, again fit for active duty, then the member shall again be put on active duty and full pay, and from the time the board of trustees shall decide that the member is fit for active duty, the member shall cease to be entitled to any payments out of the pension system because of disability for which the member was retired.