(a) The commissioners of the United States section of the Commission shall appoint one of their number as chairman, to be known as the Chairman of the United States Section of the International Joint Commission, and he shall act as chairman at all meetings of the Commission held in the United States and in respect to all matters required to be done in the United States by the chairman of the Commission.(b) The commissioners of the Canadian section of the Commission shall appoint one of their number as chairman, to be known as the Chairman of the Canadian Section of the International Joint Commission, and he shall act as chairman at all meetings of the Commission held in Canada and in respect to all matters required to be done in Canada by the chairman of the Commission.(c) In case it shall be impracticable for the chairman of either section to act in any matter, the commissioner of such section who is senior in order of appointment shall act in his stead.