The want of unity which has been pointed out tended to breed abuses specially injurious to the public, and governmental regulation was entered upon for their correction. Naturally the first attempts in this direction were made by separate States, each undertaking to regulate for itself the transportation within its own limits. Such regulation would have been perfectly logical, and perhaps effectual, had the roads within each State formed a system by themselves; but when State boundaries had very little importance, either to the roads themselves or to the traffic done over them, unless made important by restrictive and obstructive legislation, the regulation by any State must necessarily be fragmentary and imperfect, and diverse regulation in different States might be harmful rather than beneficial. It must be said for State regulation that it has in general been exercised in a prudent and conservative way, but it is liable to be influenced by a sensitive and excitable public opinion; and as nothing is more common than to find gross abuses in the matter of railroad transportation selfishly defended in localities, and even in considerable sections, which are supposed to receive benefits from them, it would not be strange if the like selfishness should sometimes succeed in influencing the exercise of power by one State in a manner that a neighboring State would regard as unfriendly and injurious. The Federal Government recently undertook the work of regulation, and in doing so accepted the view upon which the States had acted, and so worded its statute that the transportation which does not cross State lines is supposed to be excluded. The United States thus undertakes to regulate interstate commerce by rail, and the States regulate, or may regulate, that which is not interstate. It was perhaps overlooked at first that, inasmuch as Government control may embrace the making of classifications, prescribing safety and other appliances, and naming rates, any considerable regulation of State traffic and interstate traffic separately must necessarily to some extent cause interference. The two classes of traffic flow on together over the same lines in the same vehicles under the management of the same agencies, with little or no distinction based on State lines; the rates and the management influenced by considerations which necessarily are of general force, so that separate regulation may without much extravagance be compared to an attempt in the case of one of our great rivers to regulate the flow of the waters in general, but without, in doing so, interfering with an independent regulation of such portion thereof as may have come from the springs and streams of some particular section. This is one of many reasons for looking upon all existing legislation as merely tentative.