In considering the diagram of simple reproduction, we saw that its fundamental social conditions are contained in the following equation: the aggregate of means of production (the product of Department I) must be equivalent to the constant capital of both departments, but the aggregate of consumer goods (the product of Department II) must equal the sum of variable capitals _and_ surplus values of the two departments. As regards enlarged reproduction, we must now infer a precise inverse double ratio. The general precondition of enlarged reproduction is that the product of Department I must be greater in value than the constant capital of both departments taken together, and that of Department II must be so much less than the sum total of both the variable capital and the surplus value in the two departments. This, however, by no means completes the analysis of enlarged reproduction; rather has it led us merely to the threshold of the question. Having deduced the proportions of the diagram, we must now pursue their further activities, the flow of circulation and the continuity of reproduction. Just as simple reproduction may be compared to an unchanging circle, to be repeated time and again, so enlarged reproduction, to quote Sismondi, is comparable to a spiral with ever expanding loops. Let us begin by examining the loops of this spiral. The first general question arising in this connection is how actual accumulation proceeds in the two departments under the conditions now known to us, i.e. how the capitalists may capitalise part of their surplus value, and at the same time acquire the material prerequisites necessary for enlarged reproduction. Marx expounds the question in the following way: Let us assume that half the surplus value of Department I is being accumulated. The capitalists, then, use 500 for their consumption but augment their capital by another 500. In order to become active, this additional capital of 500 must be divided, as we now know, into constant and variable capital. Assuming the ratio of 4 to 1 remains what it was for the original capital, the capitalists of Department I will divide their additional capital of 500 thus: they will buy new means of production for 400 and new labour for 100. This does not present any difficulties, since we know that Department I has already produced a surplus of 500 means of production. Yet the corresponding enlargement of the variable capital by 100 units of money is not enough, since the new additional labour power must also find adequate consumer goods which can only be supplied by Department II. Now the circulation between the two large departments is shifting. Formerly, under conditions of simple reproduction, Department I acquired 1,000 consumer goods for its own workers, and now it must find another 100 for its new workers. Department I therefore engages in enlarged reproduction as follows: _4,400c + 1,100v_.