600. Agency.

Mental disorder such as to render a person incapable of acting on his own behalf incapacitates him from appointing an agent1; and a power of attorney executed by a person who is incapable of understanding what is to be effected by it is invalid2. Further, if mental incapacity supervenes during the currency of the appointment of an agent, it terminates the agency3 unless there is an agency by estoppel or holding out on which a third person dealing with the agent without knowledge of the supervening mental disorder may rely4. A representation by an agent that he is authorised