No grand jury shall make presentments of their own knowledge, upon the information of a less number than 2 of their own body, unless the juror giving the information is previously sworn as a witness, in which event, if the evidence is deemed sufficient, an indictment may be found thereon in like manner as upon the evidence of any other witness who may not be a member of the jury. The judge of the circuit court may order a special venire to be issued for a grand jury at any time when he is of the opinion that public justice requires it. The order for such venire shall be entered on the records of the court by the clerk thereof; and the clerk shall forthwith issue such venire under his signature and the seal of the court, and deliver the same to the sheriff, who shall execute the same by summoning, in the same manner now provided or that may hereafter be provided by law for summoning jurors, 16 persons, qualified by law, to constitute a grand jury. Such venire shall state the day on which such persons shall appear before the court.