In the class of conditional prohibitions, or those acts which might be done by the States with the consent of Congress, the committee of detail had placed the laying of "imposts or duties on imports." To this the Convention added "exports," in order to make the restriction applicable both to commodities carried out of and those brought into a State. But this provision, as thus arranged, would obviously make the commercial system extremely complex and inconvenient. On the one hand, the power to lay duties on imports had been conferred upon the general government, for the purposes of revenue, and to leave the States at liberty, with the consent of Congress, to lay additional duties, would subject the same merchandise to separate taxation by two distinct governments. On the other hand, if the States should be deprived of all power to lay duties on exports, they would have no means of defraying the charges of inspecting their own productions. At the same time, it was apparent that, under the guise of inspection laws, if such laws were not to be subject to the revision of Congress, a State situated on the Atlantic, with convenient seaports, could lay heavy burdens upon the productions of other States that might be obliged to pass through those ports to foreign markets. Again, if the States should be deprived of all power to lay duties on imports, they could not encourage their own manufactures; and if allowed to encourage their own manufactures by such State legislation, it must operate not only upon imports from foreign countries, but upon imports from other States of the Union, which would revive all the evils that had flowed from the want of general commercial regulations. To prevent these various mischiefs, the Convention adopted three distinct safeguards. They provided, first, by an exception, that the States might, without the consent of Congress, lay such duties and imposts as "may be absolutely necessary for executing their inspection laws"; second, that the net produce of all duties and imposts laid by any State, whether with or without the consent of Congress, shall be for the use of the Treasury of the United States; third, that all such State laws, whether passed with or without the previous consent of Congress, shall be subject to the revision and control of Congress.[306] There is, therefore, a twofold remedy against any oppressive exercise of the State power to lay duties for purposes of inspection. The question whether the particular duties exceed what is absolutely necessary for the execution of an inspection law, may be made a judicial question; and in addition to this, the law imposing the inspection duty is at all times subject to the revision and control of Congress. Any tendency to lay duties or imposts for purposes of revenue or protection, is checked by the requirement that the net produce of all duties or imposts laid by any State on imports or exports shall be