Every witness legally bound to appear as herein directed shall appear accordingly and continue to attend from day to day, and from term to term, until discharged by the court or the party who sought the summons; provided, that the continuance of a case shall not be deemed a discharge of witnesses legally bound to appear in the case so continued, and in the event of a continuance, it shall not be necessary to resummon such witnesses unless they are expressly discharged by the court or by the party at whose instance they were summoned.