If, before the conclusion of the trial, a juror becomes sick, or for other reason is unable to perform his duty, the court may order him to be discharged. In that case, if alternate jurors have been selected, one of them shall be designated to take the place of the juror so discharged. If, after all alternate jurors have been made regular jurors, a juror becomes too incapacitated to perform his duty, and has been discharged by the court, a new juror may be sworn and the trial begin anew, or the jury may be discharged and a new jury then or thereafter impaneled.