'The annual production must in the first place furnish all those objects (use-values) from which the material components of capital, used up in the course of the year, have to be replaced. Deducting these there remains the net or surplus-product, in which the surplus-value lies. And of what does this surplus-product consist? Only of things destined to satisfy the wants and desires of the capitalist class, things which, consequently, enter into the consumption fund of the capitalists? Were that the case, the cup of surplus-value would be drained to the very dregs, and nothing but simple reproduction would ever take place.--To accumulate it is necessary to convert a portion of the surplus-product into capital. But we cannot, except by a miracle, convert into capital anything but such articles as can be employed in the labour-process (i.e. means of production), and such further articles as are suitable for the sustenance of the labourer, (i.e. means of subsistence). Consequently, a part of the annual surplus-labour must have been applied to the production of additional means of production and subsistence, over and above the quantity of these things required to replace the capital advanced. In one word, surplus-value is convertible into capital solely because the surplus-product, whose value it is, already comprises the material elements of new capital.'[100] Additional means of production, however, and additional consumer goods for the workers alone are not sufficient; to get enlarged reproduction really going, additional labour is also required. Marx now finds a specific difficulty in this last condition: 'For this the mechanism of capitalist production provides beforehand, by converting the working class into a class dependent on wages, a class whose ordinary wages suffice, not only for its maintenance, but for its increase. It is only necessary for capital to incorporate this additional labour-power, annually supplied by the working class in the shape of labourers of all ages, with the surplus means of production comprised in the annual produce, and the conversion of surplus-value into capital is complete.'[101] This is the first solution which Marx gave to the problem of the accumulation of the aggregate capital. Having dwelt on this aspect of the question already in volume i of _Capital_, Marx returns to the problem at the end of the second volume of his main work whose concluding 21st chapter is devoted to accumulation and enlarged reproduction of the aggregate capital. Let us examine Marx's diagrammatic exposition of accumulation more closely. On the model of the diagram of simple reproduction with which we are already familiar, he devised a diagram for enlarged reproduction, the difference appearing most clearly if we compare the two.