The leading case under this heading is Brown _v._ Maryland,[535] decided in 1827, the issue in which was the validity of a Maryland statute requiring "all importers of foreign articles or commodities," preparatory to selling the same, to take out a license. Holding this act to be void under both article I, sec. 10, and the commerce clause, the Court, speaking through Chief Justice Marshall, advanced the following propositions: (1) that "commerce is intercourse; one of its most ordinary ingredients is traffic"; (2) that the right to import includes the right to sell; (3) that a tax on the sale of an article is a tax on the article itself--a conception of the incidence of taxation which has at times had important repercussions in other fields of Constitutional Law; (4) that the taxing power of the State does not extend in any form to imports from abroad so long as they remain "the property of the importer, in his warehouse, in the original form or package" in which they were imported--the famous "original package doctrine"; (5) that once, however, the importer parts with his importations "or otherwise mixes them with the general property of the State by breaking up his packages," the law may treat them as part and parcel of such property; (6) that even while in the original package imports are subject to the incidental operation of police measures adopted by the State in good faith for the protection of the public against apparent dangers. Lastly, in determining whether a State law amounts to a regulation of commerce the Court would, Marshall announced, be guided by "substance" and not by "form"--a proposition which has many times opened the way to extensive inquiries by the Court into the actualities both of commercial practice and of State administration.