The qualified electors of each county shall elect one Sheriff, who shall be ex-officio collector of taxes, unless otherwise provided by law; one Assessor, one Coroner, one Treasurer, who shall be ex-officio treasurer of the common school fund of the county, and one County Surveyor; for the term of two years, with such duties as are now or may be prescribed by law: Provided, that no per centum shall ever be paid to assessors upon the valuation or assessment of property by them.