The boundaries of any ambulance district established pursuant to chapter 190, which is located in a noncharter county of the first classification with a population of less than one hundred thousand which adjoins any county of the first classification with a charter form of government with a population of nine hundred thousand or more inhabitants, if such ambulance district serves any portion of a city which is located in both such counties, may be expanded so as to include the entire city within the ambulance district, but the boundaries of the district shall not be expanded beyond the city limits of such city. Such change in the boundaries of the district shall be accomplished only if seventy-five percent of the owners of any territory or tract of land within that part of the city which is not within the ambulance district file with the board a petition in writing praying that such real property be included within the district. The petition shall describe the property to be included in the district and shall describe the property owned by the petitioners and shall be deemed to give assent of the petitioners to the inclusion in the district of the property described in the petition; and such petition shall be in substantially the form set forth in section 321.495 dealing with referendums and verified in like manner.