Most of the conditions of the case are best answered by the "discount" of commercial paper as above described. The time for which such obligations have to run varies with the custom of the trade which gives rise to them, but is in most cases short enough to imply early repayment to the bank. And even where custom gives the paper longer time, if the paper itself is used only as a collateral security, the note which is the actual object of negotiation with the bank is by preference usually made not to exceed four months. It is easy then to arrange the purchases of paper with reference to the times of maturity, so as to provide for a steady succession of payments to the bank, and thus facilitate the reduction of the business, if necessary, or its direction into new channels, as prudence or good policy may require. The certainty of prompt payment at maturity, needed for this end, is presented in a high degree by the paper created in the ordinary course of business. Independently of the collateral security which the bank may hold, the written promise of a merchant or manufacturer to pay on a fixed day is an engagement which involves the credit of the promisor so far that failure is an act both of legal insolvency and of commercial dishonor. Selected with judgment, then, such paper is not only the investment which most completely answers the purposes of the bank's existence, but is probably as safe as any investment which could be found. It may easily happen, however, that the bank may find it desirable to invest a part of its resources in some other form, either because good commercial paper cannot be procured in sufficient amount, or as a matter of policy. In this case it will purchase such other securities as offer not only complete safety of investment, but the possibility of easy conversion into cash in case of need. In this country United States bonds, and many descriptions of State, municipal, and corporation bonds might answer this purpose. Stocks would more rarely answer it, being more liable to the fluctuations in price caused by misfortune or the ordinary vicissitudes of business. Mortgages on real estate, however, would not be admissible, except when held as a security, collateral to some other which is more easily convertible, for even when the mortgaged property is so ample and stable as to insure the goodness of the mortgage, the conversion of the mortgage into cash by sale is not always easy, and is especially difficult at those times when the bank most needs to have all its resources at command. Indeed, the danger to be apprehended from the locking up of resources, in securities which may be solid but are not easily realized, is so great, that it has been said to be the first duty of the banker to learn to distinguish between a note and a mortgage, his business lying with the former. Real estate, of course, cannot be regarded as a banking security, however desirable it