There is, however, another side to the story. For in one respect even the great Marshall has been in effect overruled in support of enlarged views of national authority. Without essaying a vain task of "tithing mint, anise and cummin," it is fairly accurate to say that throughout the 100 years which lie between Marshall's death and the cases of the 1930's, the conception of the federal relationship which on the whole prevailed with the Court was a competitive conception, one which envisaged the National Government and the States as jealous rivals. To be sure, we occasionally get some striking statements of contrary tendency, as in Justice Bradley's opinion in 1880 for a divided Court in the Siebold Case,[16] where is reflected recognition of certain results of the War between the States; or later in a frequently quoted dictum by Justice McKenna, in Hoke _v._ United States, in which the Mann White Slave Act was sustained in 1913: Our dual form of government has its perplexities, State and Nation having different spheres of jurisdiction ... but it must be kept in mind that we are one people; and the powers reserved to the states and those conferred on the nation are adapted to be exercised, whether independently or concurrently, to promote the general welfare, material and moral.[17] The competitive concept is, nevertheless, the one much more generally evident in the outstanding results for American Constitutional Law throughout three-quarters of its history. Of direct pertinence in this connection is the doctrine of tax exemption which converted federalism into a principle of private immunity from taxation, so that, for example, neither government could tax as income the official salaries paid by the other government.[18] This doctrine traces immediately to Marshall's famous judgment in McCulloch _v._ Maryland,[19] and bespeaks a conception of the federal relationship which regards the National Government and the States as bent on mutual frustration. Today the principle of tax exemption, except so far as Congress may choose to apply it to federal instrumentalities by virtue of its protective powers under the necessary and proper clause, is at an end.