But if the capitalists of Department I wish to accumulate half their surplus value (1,000) and to consume the other half, they need consumer goods for themselves and for their workers to the tune of 1,500 units which they can obtain only from Department II in exchange for their own products--means of production. Since Department II has already satisfied its own demand for producer goods to the extent of its own constant capital (1,430), this exchange is only possible if Department II decides to enlarge its own constant capital by 70. This means that it must enlarge its own production--and it can do so only by capitalising a corresponding part of its surplus value. If this surplus value amounts to 285 in Department II, 70 of it must be added to the constant capital. The first step towards expansion of production in Department II is thus demonstrated to be at the same time the condition for, and the consequence of, increased consumption by the capitalists of Department I. But to proceed. Hitherto, the capitalists of Department I could only spend one-half of their surplus value (500) on personal consumption. To capitalise the other half, they must redistribute these 500_s_ in such a way as to maintain at least the previous ratio of composition, i.e. they must increase the constant capital by 417 and the variable capital by 83. The first operation presents no difficulties: the surplus value of 500 belonging to the capitalists of Department I is contained in a natural form in their own product, the means of production, and is fit straightway to enter into the process of production; Department I can therefore enlarge its constant capital with the appropriate quantity of its own product. But the remaining 83 can only be used as variable capital if there is a corresponding quantity of consumer goods for the newly employed workers. Here it becomes evident for the second time that accumulation in Department I is dependent upon Department II: Department I must receive for its workers 83 more consumer goods than before from Department II. As this is again possible only by way of commodity exchange, Department I can satisfy its demands only on condition that Department II is prepared for its part to take up products of Department I, producer goods, to the tune of 83. Since Department II has no use for the means of production except to employ them in the process of production, it becomes not only possible but even necessary that Department II should increase its own constant capital by these very 83 which will now be used for capitalisation and are thus again withdrawn from the consumable surplus value of this department. The increase in the variable capital of Department I thus entails the second step in the enlargement of production in Department II. All material prerequisites of accumulation in Department I are now present and enlarged reproduction can proceed. Department II, however, has so far made only two increases in its constant capital.