_Sherman Treasury Notes._--A third form of paper money is the so-called Sherman treasury notes issued in pursuance of the act of 1890 already described. On July 1, 1921, there were $1,576,184 of them in circulation. The law declares that they shall be redeemed in _coin_, that is, either gold or silver, at the option of the government. To prevent the threatened depletion of the gold reserve[41] and provide the necessary gold with which to redeem the increasing issues of Sherman treasury notes, bond issues aggregating $262,000,000 were issued during the years 1894 and 1895. By the act of 1900 the policy of maintaining a single gold standard was definitely adopted by Congress, and it was provided that greenback notes, Sherman treasury notes, and other securities of the government should be redeemable in gold. [41] The gold reserve is a sum of money set aside for the purpose of redeeming the old "greenbacks" or United States notes. An effort has always been made to keep the amount above $100,000,000. _National Bank Notes._--The fourth class of paper money is national bank currency. A national bank, unlike other banks, not only receives deposits and makes loans and performs the other functions of banks, but also issues notes which circulate as money. There are about 8,200 national banks in the United States, with an aggregate capital of more than $1,000,000,000 and with a total circulation of $729,550,513 of notes outstanding (July 1, 1921). _Federal Reserve Notes._--The federal reserve banks, established under the act of 1913, not only receive deposits and make loans to other banks, but also have power to issue federal reserve notes which circulate as money. The amount in circulation July 1, 1921, was $2,680,494,274. This constitutes by far the largest amount of paper money in existence. The total amount of money of all kinds in circulation on July 1, 1921, amounted to $5,776,437,473, or a per capita circulation of about $53.40. =The National Bank System.=--Any number of persons, not less than five, may organize a national bank, the amount of capital required depending upon the population of the town or city where the bank is located. Prior to 1914 the organizers were obliged to purchase and deposit with the government, bonds of the United States equal to one fourth of the capital of the bank; now they may do so if they wish. The comptroller of the currency then delivers to the bank notes equal in amount to the par value of the bonds deposited. These notes when properly signed by the president and cashier of the bank may then be loaned by the bank or otherwise issued as currency, for though not a legal tender they are commonly used as money. It must also be remembered that the United States bonds deposited with the government remain the property of the bank and it receives the interest on them just as any other owner would.