The development of the productive power of labour reacts also
 on the original capital already engaged in the process of production. A
 part of the functioning constant capital consists of instruments of labour,
 such as machinery, &c., which are not consumed, and therefore not reproduced,
 or replaced by new ones of the same kind, until after long periods of time.
 But every year a part of these instruments of labour perishes or reaches
 the limit of its productive function. It reaches, therefore, in that
 year, the time for its periodical reproduction, for its replacement by
 new ones of the same kind. If the productiveness of 567labour has,
 during the using up of these instruments of labour, increased (and it develops
 continually with the uninterrupted advance of science and technology),
 more efficient and (considering their increased efficiency), cheaper machines,
 tools, apparatus, &c., replace the old. The old capital is reproduced
 in a more productive form, apart from the constant detail improvements
 in the instruments of labour already in use. The other part of the constant
 capital, raw material and auxiliary substances, is constantly reproduced
 in less than a year; those produced by agriculture, for the most part annually.
 Every introduction of improved methods, therefore, works almost simultaneously
 on the new capital and on that already in action. Every advance in Chemistry
 not only multiplies the number of useful materials and the useful applications
 of those already known, thus extending with the growth of capital its sphere
 of investment. It teaches at the same time how to throw the excrements
 of the processes of production and consumption back again into the circle
 of the process of reproduction, and thus, without any previous outlay of
 capital, creates new matter for capital. Like the increased exploitation
 of natural wealth by the mere increase in the tension of labour-power,
 science and technology give capital a power of expansion independent of
 the given magnitude of the capital actually functioning. They react at
 the same time on that part of the original capital which has entered upon
 its stage of renewal. This, in passing into its new shape, incorporates
 gratis the social advance made while its old shape was being used up. Of
 course, this development of productive power is accompanied by a partial
 depreciation of functioning capital. So far as this depreciation makes
 itself acutely felt in competition, the burden falls on the labourer, in
 the increased exploitation of whom the capitalist looks for his indemnification.