When, by reason of challenge or other cause, a sufficient number of jurors duly drawn and summoned cannot be obtained for the trial of a cause, the court shall cause jurors to be returned from the bystanders or from the county at large to complete the panel if they are on the jury not less than 7 jurors drawn and returned as provided. Such jurors shall be returned by the sheriff or his deputy or such other disinterested person as the court appoints.