http://www.marxists.org/archive/marx/works/1894-c3/ch36.htm
But the authors themselves add in a footnote:
"The advantage that would accrue from the mediation of bankers between the idle rich and the travailleurs is often counterbalanced, or even canceled, by the opportunities offered in our disorganized society to egoism, which may manifest itself in various forms of fraud and charlatanism. The bankers often worm their way between the travailleurs and idle rich for the purpose of exploiting both to the detriment of society."
Travailleur here means capitaliste industriel. Incidentally, it is wrong to regard the means at the command of the modern banking system merely as the means of idle people. In the first place, it is the portion of capital which industrialists and merchants temporarily hold in the form of idle money, as a money reserve or as capital to be invested. Hence it is idle capital, but not capital of the idle. In the second place, it is the portion of all revenue and savings in general which is to be temporarily or permanently accumulated. Both are essential to the nature of the banking system.
But it should always be borne in mind that, in the first place, money — in the form of precious metal — remains the foundation from which the credit system, by its very nature, can never detach itself. Secondly, that the credit system presupposes the monopoly of social means of production by private persons (in the form of capital and landed property), that it is itself, on the one hand, an immanent form of the capitalist mode of production, and on the other, a driving force in its development to its highest and ultimate form.
The banking system, so far as its formal organization and centralization is concerned, is the most artificial and most developed product turned out by the capitalist mode of production, a fact already expressed in 1697 in Some Thoughts of the Interests of England. This accounts for the immense power of an institution such as the Bank of England over commerce and industry, although their actual movements remain completely beyond its province and it is passive toward them. The banking system possesses indeed the form of universal book-keeping and distribution of means of production on a social scale, but solely the form. We have seen that the average profit of the individual capitalist, or of every individual capital, is determined not by the surplus-labour appropriated at first hand by each capital, but by the quantity of total surplus-labour appropriated by the total capital, from which each individual capital receives its dividend only proportional to its aliquot part of the total capital. This social character of capital is first promoted and wholly realized through the full development of the credit and banking system. On the other hand this goes farther. It places all the available and even potential capital of society that is not already actively employed at the disposal of the industrial and commercial capitalists so that neither the lenders nor users of this capital are its real owners or producers. It thus does away with the private character of capital and thus contains in itself, but only in itself, the abolition of capital itself. By means of the banking system the distribution of capital as a special business, a social function, is taken out of the hands of the private capitalists and usurers. But at the same time, banking and credit thus become the most potent means of driving capitalist production beyond its own limits, and one of the most effective vehicles of crises and swindle.
The banking system shows, furthermore, by substituting various forms of circulating credit in place of money, that money is in reality nothing but a particular expression of the social character of labour and its products, which, however, as antithetical to the basis of private production, must always appear in the last analysis as a thing, a special commodity, alongside other commodities.
Finally, there is no doubt that the credit system will serve as a powerful lever during the transition from the capitalist mode of production to the mode of production of associated labour; but only as one element in connection with other great organic revolutions of the mode of production itself. On the other hand, the illusions concerning the miraculous power of the credit and banking system, in the socialist sense, arise from a complete lack of familiarity with the capitalist mode of production and the credit system as one of its forms. As soon as the means of production cease being transformed into capital (which also includes the abolition of private property in land), credit as such no longer has any meaning. This, incidentally, was even understood by the followers of Saint-Simon. On the other hand, as long as the capitalist mode of production continues to exist, interest-bearing capital, as one of its forms, also continues to exist and constitutes in fact the basis of its credit system. Only that sensational writer, Proudhon, who wanted to perpetuate commodity-production and abolish money, [25] was capable of dreaming up the monstrous crèdit gratuit, the ostensible realization of the pious wish of the petty-bourgeois estate.