In what cases may a Government properly step in to regulate or prohibit the buying and selling of its citizens? Hundreds of inductions extending through hundreds of years have been carefully and logically conducted in order to reach a just and comprehensive answer to this question; and in all probability the cases have been inductively ascertained for all time, and they are these: _such buying and selling may be controlled and prohibited, as are proven to be contrary_ (1) _to the public Morals_, (2) _to the public Health_, (3) _to the public Revenue_. All other buying and selling may be safely assumed to be both profitable to the parties to it, and also useful to the Commonwealth in general; and any interference with it by public authority is a high-handed infringement of natural rights, a blow aimed at the life and source of property. These wrongful strokes at private rights, this restriction on the freedom of individuals to exchange products for their own welfare, is now mostly confined in civilized countries to the region of Taxation. Within this region the wrongs are still frightful. Judge Cooley, in his "Principles of Constitutional Law," states the matter as follows: "_Constitutionally a tax can have no other basis than the raising of revenue for public purposes; and whatever governmental action has not this basis is tyrannical and unlawful. A tax on imports, therefore, the purpose of which is not to raise a revenue, but to discourage and indirectly prohibit some particular import for the sake of some home manufacturer, may well be questioned as being merely colorable, and therefore not warranted by constitutional principle._"