The tax assessor or his deputy or any other officer administering the oath to the person making the return of property for taxation must orally administer the following oath to every taxpayer before making his returns: “You do solemnly swear that you will true answers make to all lawful questions which may be put to you touching the return you are about to make and that you will make a full and complete return of all property owned by you or in which you had any interest whatever or of which you were trustee or agent on the first day of October of the present tax year, and this return is made upon your personal knowledge, so help you God.”