(_a_) The product of Department I equals in value the sum of the two constant capitals in Departments I and II. (_b_) The constant capital of Department II equals the sum of variable capital and surplus value in Department I--a necessary consequence of (_a_). (_c_) The product of Department II equals the sum of variable capital and surplus value in both departments--a necessary consequence of (_a_) and (_b_). These equations correspond to the conditions of capitalist commodity production (at the restricted level of simple reproduction, however). Equation (_b_), for instance, is a result of the production of commodities, entailed by the fact, in other words, that the entrepreneurs of either department can only obtain the products of the other by an exchange of equivalents. Variable capital and surplus value in Department I together represent the demand of this department for consumer goods. The product of Department II must provide for the satisfaction of this demand, but consumer goods can only be obtained in exchange for an equivalent part of the product of Department I, the means of production. These equivalents, useless to Department II in their natural form if not employed as constant capital in the process of production, will thus determine how much constant capital there is to be in Department II. If this proportion were not adhered to, if, e.g., the constant capital of Department II (as a quantity of value) were larger than I(_v + s_), then it could not be completely transformed into means of production, since the demand of Department I for consumer goods would be too small; if the constant capital (II) were smaller than I(_v + s.c_), either the previous quantity of labour power could not be employed in this department, or the capitalists could not consume the whole of their surplus value. In all these cases, the premises of simple reproduction would be violated.