[Karl Marx] came across many instances of low-paid workers but he never succeeded in unearthing one who was paid literally no wages at all. Yet such a worker did exist, in his own household. (...) This was Helen Demuth, known in the family as 'Lenchen'. Born in 1823, of peasant stock, she had joined the von Westphalen family at the age of eight as a nursery-maid. She got her keep but was paid nothing. In 1845 the Baroness, who felt sorrow and anxiety for her married daughter, gave Lenchen, then twenty-two, to Jenny Marx to ease her lot. She remained in the Marx family until her death in 1890. (...) She was a ferociously hard worker, not only cooking and scrubbing but managing the family budget, which Jenny was incapable of handling. Marx never paid her a penny.

Paul Johnson "Intellectuals", Harper Perennial, 1992, p.79