completes the circulation of this quantity of money for the moment, but the circulation within society has not yet come to an end. The capitalists of Department I have not yet realised their surplus value to buy consumer goods for themselves; it is still contained in their product in a form which is of no use to them. Moreover, the capitalists of Department II have not yet renewed the second half of their constant capital. These two acts of exchange are identical both in substance and in value, for the capitalists of Department I receive their goods from Department II in exchange for the I(1,000_c_) means of production needed by the capitalists of Department II. However, a new quantity of money is required to effect this exchange. It is true that the same money which has already completed its course, might be brought into circulation again for this purpose--in theory, there could be no objection to this. In practice, however, this solution is out of the question, for the needs of the capitalists, as consumers, must be satisfied just as constantly as the needs of the workers--they run parallel to the process of production and must be mediated by specific quantities of money. Hence it follows that the capitalists of both departments--that is to say all capitalists--must have a further cash reserve in hand, in addition to the money required as variable capital, in order to realise their own surplus value in the form of consumer goods. On the other hand, before the total product is realised and during the process of its production, certain parts of the constant capital must be bought continually. These are the circulating parts of the constant capital, such as raw and auxiliary materials, semi-finished goods, lighting and the like. Therefore, not only must the capitalists of Department I have certain quantities of money in hand to satisfy their needs as consumers, but the capitalists of Department II must also have money to meet the requirements of their constant capital. The exchange of 1,000s I (the surplus value of Department I contained in the means of production) against goods is thus effected by money which is advanced partly by the capitalists of Department I in order to satisfy their needs as consumers, and partly by the capitalists of Department II in order to satisfy their needs as producers.[91] Both lots of capitalists may each advance 500 units of the money necessary for the exchange, or possibly the two departments will contribute in different proportions. At any rate, two things are certain: (_a_) the money set aside for the purpose by both departments must suffice to effect the exchange between I(1,000_s_) and II(1,000_c_); (_b_) whatever the distribution of this money between the two departments may have been, the exchange transaction completed, each department of capitalist production must again possess the same amount of money it had earlier put into circulation. This latter maxim applies quite generally to social