The county commissioners shall appoint a county solicitor, who shall be an attorney-at-law admitted to practice in the courts of this Commonwealth and may be one person or a law firm, partnership, association or professional corporation. Before entering upon the duties of office, the solicitor shall file with the county commissioners an agreement to pay all fees, attorney's fees, and commissions received from every source as county solicitor into the county treasury.
16 P.S. § 901