In tracing the evolution of money we have seen that primarily it performs two important functions - as a medium of exchange and as a measure or standard of value. Its function as a medium of exchange is to serve as a go-between in the exchange of commodities. The medium of exchange of most modern countries is quite complex and of various kinds adapted to different scales of payment. Generally the medium of exchange comprises coins of different metals and denominations issued by the government; paper money issued by the government or by the banks, or by both; and credit instruments, such as checks, drafts, bills of exchange, letters of credit and the like issued under private or public authority. Some of these media are widely and freely current throughout the community, passing freely from hand to hand in settlement of exchanges large and small. To this class belong metallic money or coins both standard and subsidiary, coin certificates, government notes and bank notes. This hand-to-hand money, however, constitutes only a small part of the medium of exchange of a highly developed commercial country. Of much larger importance, though having but limited circulation, are such media as checks and drafts which represent bank deposits and which are transferred between other than the original parties only by indorsement. This group includes also commercial bills of exchange, domestic and foreign, representing goods; and postal and express money orders, travelers' cheques and letters of credit. Book accounts by means of which purchases and sales are balanced against each other, directly or indirectly, constitute the most important element of the medium of exchange.