Section 7. County officers -- Salaries. All county officers and deputies when allowed, shall receive, as full compensation for their services, fixed annual salaries, to be paid monthly out of the county treasury, as other expenses are paid. All actual and necessary expenses incurred by any county officer or deputy in the performance of his official duties, shall be a legal charge against the county, and may be retained by him out of any fees which may come into his hands. All fees which may come into his hands from whatever source, over and above his actual and necessary expenses, shall be turned into the county treasury at the end of each quarter. He shall at the end of each quarter, file with the clerk of the board of county commissioners, a sworn statement, accompanied by proper vouchers, showing all expenses incurred and all fees received, which must be audited by the board as other accounts.