Section 12. (a) The county officers shall be paid only the salary provided herein for services performed for the county or any other governmental unit: Provided, however, That this restriction shall not apply to those county officers receiving a salary as executive and administrative officers of institution districts existing in their counties.
(b) All fees and commissions received in the conduct of any county office shall be paid directly to the county. Fees shall not be deemed to include reimbursement for mileage.