Of the thirty thousand or more banks in the United States, twenty-eight thousand or so are known as commercial banks, and it may be said that it is upon the success or failure of their operations that the prosperity of the nation is closely bound up. Commercial banks may be considered as credit institutions and as the country's credit managers. Their purpose consists in mobilizing the country's reserves, and so using them as to make them most productive and of most benefit to the country. Unlike the operations of savings banks, with their secured character and unfluctuating conditions coincident with a savings and conservative population, the commercial banks cannot and neither are they at law permitted to tie up their funds in long time investments. The nature of their business and the very basis of their existence is in rendering the maximum of service to the business community. A depositor may have entrusted only yesterday to a bank the keeping of a sum of one hundred thousand dollars, not knowing at which time he will find it necessary to use the funds. A day or so later there may present itself an opportunity for him to take advantage of, and he may thus be required to use such funds to materialize his purpose. This may necessitate the withdrawal of a large part of his deposit amount, which may be the case with a thousand and one depositors of the same bank. It is, therefore, apparent that even in its regular course of business, the operations of the commercial bank are far different from the investment bank. It must be enabled at any time to convert its assets, in whatever form, into ready funds. Liquidity of assets is as important in a commercial bank's operations as security of assets.