12. A member may appoint any other member of the section of which he is a member as his proxy for voting at a General Meeting where a poll is demanded and taken. Such an appointment shall be made by an instrument of proxy in the form hereinafter provided or to the like effect and shall be signed by the member appointing the proxy and shall be left with the Secretary or at his office at least 48 hours before the time appointed for holding the meeting therein specified and shall be available only for that meeting and any adjournment thereof.