Walras introduced his fixed coefficients of production as a preliminary device (Section 204) but never realized a definitive generalization. Since he eventually wished to study the consequences of growth of the economy (more people disposing of more than proportionally more products) with a fixed quantity of land, the fiction of fixed coefficients of production could not be maintained. This means that the coefficients of production had to be replaced by variable coefficients. Walras never revised his formal mathematical models in this sense. He only studied marginal productivity and its dependence on the scale of production as an afterthought, in Part VII of the Eléments. Nevertheless, the topic is interesting enough to deal with.