They do not react directly upon cash holdings. If a government aims at increasing the amount of cash kept by its subjects, it must order them to deposit a certain amount with an office and to leave it there untouched. But if the government were simply to obstruct the importation of goods and the exportation of money, it would fail to attain its goal. If imports drop, other things being equal, exports drop concomitantly. The role money plays in international trade is not different from that which it plays in domestic trade.
Money is no less a medium of exchange in foreign trade than it is in domestic trade.
Both in domestic trade and in international trade purchases and sales result in a more than passing change in the cash holdings of individuals and firms only if people are purposely intent upon increasing or restricting the size of their cash holdings. A surplus of money flows into a country only when its residents are more eager to increase their cash holdings than are the foreigners. An outflow of money occurs only if the residents are more eager to reduce their cash holdings than are the foreigners. A transfer of money from one country into another country which is not compensated by a transfer in the opposite direction is never the unintended result of international trade transactions. It is always the outcome of intended changes in the cash holdings of the residents.