Marx has discussed two functions of money: (1) as measure of exchange value, i.e. as unit of price, and (2) as medium of circulation. He now comes to a third, inserting the heading: “(c) Money as material representative of wealth (accumulation of money; before that, money as the general material of contracts, etc.)”.

“It is in the nature of circulation that every point appears simultaneously as a starting-point and as a conclusion, and, more precisely, that it appears to be the one in so far as it appears to be the other.” Seen from this point of view, the movement C-M-M-C appears “just as correct” as M-C-C-M. In the process C-M-M-C, under the assumption that one quantity of labour-time is exchanged for another of the same magnitude, the actual quantity of money involved is irrelevant.

More (pdf, 269 KB): The Chapter on Money Part 7: Money as the Material Representative of Wealth (pp. 203-225)