The county governing body of the county comprising the Thirty-seventh Judicial Circuit is hereby authorized, and empowered to pay, in the discretion of the county governing body, an annual county salary supplement of an amount equal to one thousand dollars ($1,000) less than the annual county salary supplement paid to the circuit judges of the Thirty-seventh Judicial Circuit. The supplement hereby authorized shall be paid in equal monthly installments out of the general fund in the county treasury, shall be in addition to the salary paid the district attorney by the State of Alabama, and shall be in addition to any other county expense allowance or supplement heretofore provided by law which is payable from the county.