The St. Louis County attorney may appoint, with the consent of the county board, assistant county attorneys and clerical help at such salaries as may be determined by the board. Those heretofore appointed shall be designated assistant county attorneys. They shall take the official oath of office and execute a bond in the same manner as the county attorney, said bonds to be paid by the county. The assistant county attorneys shall be fully authorized to do and perform the duties pertaining to the office as directed by the county attorney. The assistant county attorneys shall be paid semimonthly as is now done, and shall be reimbursed for their actual expenses and mileage according to law when on official business for the county.