Such was the condition of the law when the act of 1875 was passed, which allowed suits to be brought by the assignees of promissory notes negotiable by the law-merchant, as well as of foreign and domestic bills of exchange, if the necessary citizenship of the parties existed. This opened wide the door for frauds upon the jurisdiction of the court by collusive transfers, so as to make colorable parties and create cases cognizable by the courts of the United States. To protect the courts as well as parties against such frauds upon their jurisdiction, it was made the duty of a court, at any time when it satisfactorily appeared that a suit did not 'really and substantially involve a dispute or controversy' properly within its jurisdiction, or that the parties 'had been improperly or collusively made or joined * * * for the purpose of creating a case cognizable' under that act, 'to proceed no further therein,' but to dismiss the suit or remand it to the state court from which it had been removed. This, as was said in Williams v. Nottawa, 104 U.S. 211, 'imposed the duty on the court, on its own motion, without waiting for the parties, to stop all further proceedings and dismiss the suit the moment a fraud on its jurisdiction was discovered.' The old rule established by the decisions, which required all objections to the citizenship of the parties, unless shown on the face of the record to be taken by plea in abatement before pleading to the merits, was changed, and the courts were given full authority to protect themselves against the false pretenses of apparent parties. This is a salutary provision which ought not to be neglected. It was intended to promote the ends of justice, and is equivalent to an express enactment by congress that the circuit courts shall not have jurisdiction of suits which do not really and substantiall involve a dispute or controversy of which they have congizance, nor of suits in which the parties have been improperly or collusively made or joined for the purpose of creating a case cognizable under the act. It does not, any more than did the act of 1789, prevent the courts from taking jurisdiction of suits by an assignee when the assignment is not fictitious and actually conveys all the interest of the assignor in the thing assigned, so that the suit when begun involves really and substantially a dispute or controversy in favor of the assignee for himself and on his own account against the defendant; but it does in positive language provide that, if the assignment is collusive, and for the purpose of enabling the assignee to sue in the courts of the United States for the benefit of the assignor, when the assignor himself could not bring the action, the court shall not proceed in the case. In this respect it goes further than the rulings of the courts under the act of 1789. Under its provisions the holders of promissory notes, or of foreign or domestic bills of exchange, who are citizens of a state in which the decisions of the courts have been adverse to their interests, cannot, by collusive transfers to citizens of other states, create a case apparently cognizable in the courts of the United States, and have it prosecuted by their assignees in those tribunals for their benefit, in the hope of securing an adjudication in that jurisdiction more favorable to their interests. The courts of the United States were not created under the constitution for any such purpose. Except in certain specified cases they have no jurisdiction of controversies between citizens of the same state.