State inspection laws, health laws, and laws for regulating the internal commerce of a State, and those which respect turnpike roads, ferries, &c. are not within the power granted to Congress. ... Inspection laws, quarantine laws, health laws of every description, as well as laws for regulating the internal commerce of a State, and those which respect turnpike roads, ferries, &c., are component parts of this mass. No direct general power over these objects is granted to Congress, and, consequently, they remain subject to State legislation.
John MarshallWhen a law is in its nature a contract, when absolute rights have vested under that contract, a repeal of the law cannot divest those rights.
John MarshallThe peculiar circumstances of the moment may render a measure more or less wise, but cannot render it more or less constitutional.
John Marshall