Section 34. No extension of the mortgage, and no acknowledgment that the mortgage is not satisfied, whether contained in a conveyance or in a separate instrument, shall be sufficient to extend the period specified in section thirty-three unless it is executed by one or more of the person or persons then appearing of record to own the real estate then subject to the mortgage, and describes the mortgage sufficiently to identify the record of it, and states that the property is subject to the mortgage or that the mortgage is not satisfied. No affidavit that the mortgage is not satisfied shall be sufficient to extend the period unless it is executed by the holder of the mortgage, describes the mortgage sufficiently to identify the record thereof, names one or more of the person or persons then appearing of record to own the real estate then subject to the mortgage, and states that the mortgage remains unsatisfied, and if the mortgage secures a promissory note or sum of money, the amount believed to remain unpaid. The holders of mortgages or other encumbrances shall not be considered owners. The register of deeds upon payment of the fee required by law shall record any such affidavit and any such acknowledgment contained in a separate instrument, and enter upon the margin of the record of the mortgage a note of reference to the record of the affidavit or acknowledgment and index it in the grantor index under the names of the owner or owners named in the affidavit or executing the acknowledgment.