The Wealth of Nations by Part 2 Chapter 2 Page 43

the same. The banks, when their customers apply to them for money, generally advance it to them in their own promissory notes.

These the merchants pay away to the manufacturers for goods, the manufacturers to the farmers for materials and provisions, the farmers to their landlords for rent, the landlords repay them to the merchants for the conveniencies and luxuries with which they supply them, and the merchants again return them to the banks in order to balance their cash accounts, or to replace what they may have borrowed of them; and thus almost the whole money business of the country is transacted by means of them. Hence the great trade of those companies.

By means of those cash accounts every merchant can, without imprudence, carry on a greater trade than he otherwise could do.