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 QUARANTINE LAWS. 297

enacted in the execution of acknowledged State powers, interfere with, or are contrary to, the laws of Congress made in pursuance of the Constitution, or some treaty made under the authority of the United States. In every such case the act of Congress, or the treaty, is supreme ; and the law of the State, though enacted in the exercise of powers not controverted, must yield to it/* In that case the law of New York granting to Fulton and Livingston the monopoly of navigation by steam in the State waters was held void, as conflicting with the laws of the United States licensing the navigation of those waters. To take one other example : a State law authorized a bridge, which interfered with the passage of steamboats, to be constructed across a river flowing through several States. The law was held unconstitutional on the ground that commerce upon the river had been regulated by express con- gressional legislation.^ Just as it is possible for Congress by express legislation to deprive the States of some of the power to regulate commerce which they previously possessed, so Congress can indicate by express legislation its will that a State shall not be deprived of the right to enact certain regulations of commerce previously permissible and constitutional. This, Congress has done in case of pilotage^ and quarantine laws.^ Congress can by adoption make valid a hitherto unconstitutional State regulation of commerce.* But it would seem that Congress cannot authorize commercial legislation by the States, for this would be a delegation by Congress of its powers.^ It may be added that when Congress has by statute regulated a given subject, the statute would gener- ally be construed to have expressed the whole mind of Congress upon that subject, so that any additional or supplementary laws by the States would be in conflict with the regulation exercised by Congress.

When, however, there is no express legislation upon the subject, the question whether Congress has exercised its power of regulation over it becomes more difficult ; for the inaction of Congress has to

1 The first Wheeling Bridge case, Slate of PennsyWania v. The Wheeling Bridge Co., 13 How. 518 (1851).

2 U. S. Rev. Stat. 4235; Cooley v. Port Wardens, /w/, p. 298.


 * U. S. Rev. Stat., Title Iviii. ; Morgan v, Louisiania, post, p. 300.

Belmont Bridge Co., 1 8 How. 421 (1855).
 * Compare the second Wheeling Bridge case. State of Pennsylvania v. Wheeling &

upon in the decision. See, also, Gibbons v, Ogden, 9 Wheat. I, 207.
 * See Cooley v. Port Wardens, 12 How. 299 (1857). This point was not passed