90.—(1) Unless the comptroller otherwise directs in any particular case—
(a)all attendances upon him may be made by or through an agent; and
(b)every notice, application or other document filed under the Act may be signed by an agent.
(2) Where after a person has become a party to proceedings before the comptroller he appoints an agent for the first time or appoints one agent in substitution for another, the newly appointed agent shall file Patents Form 51/77 in duplicate on or before the first occasion when he acts as agent.