Let us assume that the constant capital, 6,000_c_, in the two departments, which is in fact absorbed by the annual product of these departments, consists of 1,500_c_ fixed and 4,500_c_ circulating capital, the 1,500_c_ of fixed capital representing here the annual wear and tear of the premises, machinery and labouring cattle. This annual wear and tear equals, say, 10 per cent of the total value of the fixed capital employed. Then the total social capital would really consist of _19,500c + 1,500v_, the constant capital in both departments being 1,500_c_ of fixed and 4,500_c_ of circulating capital. Since the term of life of the aggregate fixed capital, with a 10 per cent wear and tear, is ten years _ex hypothesi_, the fixed capital needs renewal only after the lapse of ten years. Meanwhile one-tenth of its value enters into social production in every year. If all the fixed capital of a society, with the same rate of wear and tear, were of equal durability, it would, on our assumption, need complete renewal once within ten years. This, however, is not the case. Some of the various use-forms which are part of the fixed capital may last longer and others shorter, wear and tear and duration of life are quite different in the different kinds and individual representations of fixed capital. In consequence, fixed capital need not be renewed--reproduced in its concrete use-form--all at once, but parts of it are continually renewed at various stages of social production, while other parts still function in their older form. Our assumption of a fixed capital of 15,000_c_ with a 10 per cent rate of wear and tear does not mean that this must be renewed all at once every ten years, but that an annual average renewal and replacement must be effected of a part of the total fixed social capital corresponding to one-tenth of its value; that is to say, Department I which has to satisfy the needs of society for means of production must reproduce, year by year not only all its raw and partly finished materials, etc., its circulating capital to the value of 4,500, but must also reproduce the use-forms of its fixed capital--premises, machinery, and the like--to the extent of 1,500, corresponding with the annual wear and tear of fixed capital. If Department I continues in this manner to renew one-tenth of the fixed capital in its use-form every year, the result will be that every ten years the total fixed capital of society will have been replaced throughout by new items; thus it follows that the reproduction of those parts disregarded so far is also completely accounted for in the above scheme.