“ It is only where rights, in themselves appropriate subjects of judicial cognizance, are being, or about to be, affected prejudicially by the application or enforcement of a statute that its validity may be called in question by a suitor and determined by an exertion of the judicial power. ”

“ If the state have a right to sue to annul these orders, a familiar rule requires that it shall proceed with due regard for the rights of the carriers who have put the orders into effect and are conforming to them. On the question whether the orders are invalid and should be annulled, or are valid and should be upheld, the carriers are entitled to be heard. Their interests are directly involved and will be necessarily affected by the outcome. They are not parties to the bill, and as to all but one the bill makes it clear that their citizenship is an obstacle to making them such. ”

“ The provisions relating to the Interstate Commerce Commission these are in title IV-may be summarized as investing the Commission with a substantial measure of control or supervision over interstate rates and fares; over the removal of any undue or unreasonable advantage, preference or prejudice, as between persons or localities in intrastate commerce on the one hand and in interstate commerce on the other, arising from intrastate rates and fares; over the removal of any undue, unreasonable or unjust discrimination against interstate commerce caused by intrastate rates and fares ”