There can be but little question that the chief and possibly the entire purpose of,the Commerce Clause was, with reference to interstate commerce, to empower the federal authorities to prevent the States from interfering with the freedom of commercial intercourse between themselves; but, as the court observe in Addyston Pipe & Steel Co. v. United States,4 " The reasons which may have caused the framers of the Constitution to repose power to regulate interstate commerce in Congress do not affect or limit the extent of the power itself." That is to say, the power being granted without qualification, except as to preference of the ports of one State over those of another, extrinsic evidence may not be resorted to in order to give to the grant a meaning narrower than that which its words convey.

3 The Commerce Clause of the Federal Constitution (1898), p. 14.

4 175 U. S. 211; 20 Sup. Ct. Rep. 96; 44 L. ed. 136.