In Bankers Life & Casualty Co. v. Holland, 346 U.S. 379, 74 S.Ct. 145, 98 L.Ed. 106 (1953), the district court had severed an action for treble damages under an antitrust act as to one defendant, and transferred the cause as to him to the district where he lived. The opposing party sought mandamus to compel the judge to set aside the order. The Supreme Court held, that inasmuch as the district court had jurisdiction both of the subject matter of the suit and of the person, it became necessary and proper for it to rule upon the issue raised in the due course of the litigation. The Court, 346 U.S. at page 382, 74 S.Ct. at page 147, said: "The ruling on a question of law decisive of the issue presented by Cravey's motion and the replication of the petitioner was made in the course of the exercise of the court's jurisdiction to decide issues properly brought before it. Ex parte American Steel Barrel Co., 1913, 230 U.S. 35, 45-46, 33 S.Ct. 1007, 1010, 1011, 57 L.Ed. 1379; Ex parte Roe, 1914, 234 U.S. 70, 73, 34 S.Ct. 722, 723, 58 L. Ed. 1217."