Section 25. On the day when jurors are summoned to attend at court for the trial of civil or criminal cases, except capital cases, the clerk of the court shall cause the name, together with the information provided for in sections four and five, of each person so summoned to be written on separate ballots, substantially of uniform size, and shall cause them to be placed in a box provided therefor, unless such information is otherwise available in the courtroom on a list prepared for that purpose. When a case is ready for trial the clerk in open court, after shaking the ballots thoroughly, shall draw them out in succession until the names of twelve or such greater number as the court may order under section twenty-six B are drawn who appear and are not excused or set aside. For trials by juries of six the clerk shall draw said ballots in succession until the names of six or such greater number as the court may order under section twenty-six B are drawn who appear and are not excused or set aside. The persons so drawn shall be duly sworn and impanelled and, subject to said section twenty-six B, shall be the jury to try the issue, and one of them shall be appointed foreman by the court. The ballots containing names of the jurors so sworn shall be kept apart by the clerk until the verdict of such jury has been recorded or such jury has been discharged, when such ballots shall be returned to the box. If a case is ready for trial before the verdict in the preceding case has been recorded or the jury discharged, the court may order a jury for the trial of such issue to be impanelled by the drawing in the manner aforesaid of ballots from those remaining in the box.