, than controlling them: but that they may be legitimately controlled for these ends, is in principle undeniable. On the other hand, there are questions relating to interference with trade, which are essentially questions of liberty; such as the Maine Law, already touched upon; the prohibition of the importation of opium into China; the restriction of the sale of poisons; all cases, in short, where the object of the interference is to make it impossible or difficult to obtain a particular commodity. These interferences are objectionable, not as infringements on the liberty of the producer or seller, but on that of the buyer.