But, even where a part of the constant capital is not reproduced directly from the output of the industry itself, it may be similarly reproduced by a direct exchange with some other industry, so that both mutually replace their constant capital out of their joint production. For example, cotton waste can be fed on to the fields as fertiliser. Cotton is constant capital for the spinner, and fertiliser is constant capital for the cotton grower. So, the spinner may obtain a quantity of cotton from the cotton grower in direct exchange for a quantity of cotton waste used as fertiliser.
“In general, however, there is a cardinal difference between the production of machines and primary production (of raw materials: iron, wood, coal) and the other phases of production: in the latter, there is no interaction between them. Linen cannot be a part of the spinner’s constant capital, nor can yarn (as such) be part of the constant capital of the flax-grower or machinery manufacturer. But the raw material of machinery— apart from such agricultural products as leather belting, rope, etc. —is wood, iron and coal, while on the other hand machinery in its turn enters as a means of production into the constant capital of the producers of wood, iron, coal, etc. In fact, therefore, both replace each other a part of their constant capital in kind, Here there is exchange of constant capital for constant capital.” (p 145)
The fact that this exchange is mediated by money, does not change this reality. It merely obscures the underlying relations whereby there is an exchange of capital with capital, rather than an exchange of capital with revenue. In supplying cotton waste to the cotton grower, the spinner does not receive revenue in return, i.e. consumption goods, They receive constant capital themselves in the shape of cotton.
If they supply cotton waste of £10 to the grower and get paid £10 in money for it, this changes nothing, because they then hand this £10 back to the grower, in exchange for £10 of cotton. If the cotton spinner grew their own cotton, the actual situation here would be even clearer, that they would, in this process have simultaneously replaced their constant capital (fertiliser) and their constant capital (cotton) out of their own production, with none of this output being thrown into circulation in exchange for consumption goods (revenue), and no income being produced by it. All that has happened is that a quantity of constant capital consumed in production has been replaced out of that production. Its value transferred into the value of current production has been reproduced out of current production, just as its use value consumed in production has been directly replaced in kind from that production.