_Effects experienced within Economic Society from Interchanges with the Environing Area._--The introduction of improved methods of production within the central area usually calls for an expenditure of capital there, and this is largely furnished from the net profits from previous economies in production, and will, in its turn, furnish net profits that will convert themselves into the capital needed for applying future inventions. The study of the causes of an increase of capital, as well as of each of the generic changes that are going on within the center we defer for later chapters; but at present we need to know that the changes going on within what we define as economic society are affected by the intercourse which that society maintains with its environment. Immigration across the outer boundary of the general division enhances the rapidity of growth of the population within it, while emigration reduces it. Exporting capital in itself reduces the rate of accumulation at home, and importing increases it. Introducing into foreign regions economical methods in use at home, modifies the trade which goes on between the great areas, and there is a perpetual rivalry between the direct and the indirect process of obtaining goods at home. When a unit of labor can directly make more of _A'''_ than it can procure by making _A_ and exchanging it abroad for _A'''_, the manufacture of _A'''_ is legitimate and profitable, but when the unit of labor can procure more of _A'''_ by the indirect process in which an exchange with a foreign region intervenes, static law requires that this indirect process be resorted to. We should make _A_ and buy _A'''_ in order to get the most of the latter commodity. This is the essence of the time-honored argument for freedom of trade, but the conclusion to which it leads is modified by a consideration of further dynamic influences which will, in due time, be presented.