Power to summon material witness, or examine person present. Any Court may, at any stage of any inquiry, trial or other proceeding under this Code, summon any person as a witness, or examine any person in attendance, though not summoned as a witness, or. recall and re- examine any person already examined and the Court shall summon and examine or recall and re- examine any such person if his evidence appears to it to be essential to the just decision of the case.