Section 65. If a corporation is a party, the adverse party may examine the president, treasurer, clerk or a director, manager or superintendent, or other officer thereof, as if he were a party. If a municipal corporation is a party, the mayor or the chairman of the board of selectmen may be examined as if he were a party, except that no city or town official shall be interrogated concerning matters of public record. If a minor or person under guardianship is a party, the adverse party may examine as if said party were not a minor or under guardianship; provided, that if the minor be not of such age as to appreciate an oath, or the person under guardianship be mentally incompetent to answer, the person appearing in the suit as the guardian, guardian ad litem or next friend of such party shall make answer.