The county recorder in any county now having, or which may hereafter have, a population of 400,000 or over, and in which the business of the registrar of titles is conducted in a separate place from that of the county recorder, shall provide a tract index of all lands registered under what is known as the Torrens System of land titles, and the same shall be kept in the office of the county recorder in any such county for the use of receiving clerks in checking the properties listed therein with the properties described in the instruments presented for record.