By the Interstate Commerce Act of 1887 interstate railroads are forbidden to form combinations or "pools" for the maintenance of rates, whether for freight or passenger traffic. By the act of July 2, 1890, entitled "An Act to Protect Commerce Against Unlawful Restraints and Monopolies," a general prohibition is laid upon "every contract, combination in the form of trust or otherwise, or conspiracy in restraint of trade or commerce among the several States, or with foreign nations." In United States v. Trans-Missouri Freight Association27 the railroads are held to be included within this general prohibition.

Based upon alleged violations of this act of 1890 a series of suits have been brought and have received final adjudication by the Supreme Court. For the decision of these cases the court has found it necessary to consider more carefully than in any other set of cases the question what constitutes interstate commerce, and what, therefore, are the limits of the federal regulative power under the Commerce Clause. Thus, though it cannot be said that these cases have necessitated the enunciation of constitutional doctrines not elsewhere stated, or already considered in this treatise, they have resulted in specific adjudications which serve to set in the clearest light the extent and limits of the federal commercial power. For this reason it is advisable to consider these cases seriatim.

26 In this section only those portions of the act, and those judicial decisions arising thereunder, are considered which have given rise to constitutional questions.

27 166 U. S. 290; 17 Sup. Ct. Rep. 540; 41 L. ed. 1007.