Keogh v. Chicago & N.W.R. Co., 260 U.S. 156, 43 S.Ct. 47, 67 L.Ed. 183. (4) It is said that persons other than the United States are barred from enjoining violations of the antitrust laws by virtue of ?? 16 of the Clayton Act. 38 Stat. 737, 15 U.S.C. ?? 26, 15 U.S.C.A. ?? 26.