If then the unnatural extension of the working day, that capital necessarily strives after in its unmeasured passion for self expansion, shortens the length of life of the individual labourer, and therefore the duration of his labour power, the forces used up have to be replaced at a more rapid rate and the sum of the expenses for the reproduction of labour power will be greater; just as in a machine the part of its value to be reproduced every day is greater the more rapidly the machine is worn out.