Capital, Volume Three: The Process of Capitalist Production as a Whole by Karl Marx

It has been shown that the value of commodities, or the price of production regulated by their total value, resolves itself into:

1) A portion of value replacing constant capital, or representing past labour, which was used up in the form of means of production in making the commodity; in a word, the value, or price, which these means of production carried into the production process of the commodities. We are not referring at all here to individual commodities, but to commodity-capital, that is, the form in which the product of the capital during a definite period of time, say a year, manifests itself; the individual commodity forms one element of commodity-capital, which, moreover, so far as its value is concerned, resolves itself into the same analogous constituents.