International exchange is not really different from the domestic exchanges which go on within a nation. The foreigner who has some product of his own to exchange against a product of ours deals as a private man with other private men, and if you could see all the exchanges of the world going on you would not distinguish between the character of an exchange, say, between Devonshire and London and one between London and the Argentine. The Devonshire man grows wheat, which he sells perhaps in a London market, and buys manufactured products which a merchant in London provides. The farmer in the Argentine does much the same thing, sells wheat and receives in exchange what manufactures he needs, precisely as though he were living in Devonshire instead of abroad. He does not trade with “England,” but with a particular merchant or company in England. But there are certain points about international trade which one must get clear unless one is to make mistakes in the political problems arising out of it. In the first place, international trade is always subject to a certain interference which domestic trade does not suffer. All countries have a _tariff_, that is a set of taxes upon a great number of the articles coming in from abroad. Even those countries which, as England did until quite lately, believe in leaving their citizens on equal terms with foreign competitors and have gone in for complete free trade, examine all goods at the port of entry or at special points on the frontier, both in order to raise revenue and to keep out undesirable goods, such as certain drugs; nor does any country allow _all_ things to come in unexamined, lest forbidden things should come in unobserved. Moreover, it is important to measure the nature and volume of a nation’s foreign trade, and this cannot be done without stopping things at the ports or frontiers and examining them.