The various functions of a bank are largely a matter of usage as established by judicial decision. The matters of deposit, discount and issue will be treated under appropriate heads. But there are yet other transactions in which banks have sometimes become engaged which have required the judgment of the courts as to whether they were within the powers of a bank or not." Since the governing statute or charter generally defines the powers of a bank by general phrases, such as " the business of banking," or a "general banking business," the courts must in such cases be guided by the limits of the business as defined by general custom or the decisions of courts. Custom may be appealed to to show that an act is within the ordinary business of a bank.1 Whenever the statute or the charter permits an act to be done by a bank, the terms of the statute or charter must govern. The same rule holds as to acts forbidden to a bank. The governing statute or charter may forbid an act by implication as well as by a direct prohibition, as in the case of national banks, which are by the terms of the national bank act impliedly forbidden to loan on real-estate security. The effect of an unauthorized act of banking has already been discussed.2