sian" swings of effective demand run to and fro over the long-term evolution. The control of production may in principle be appropriate to any social and political system - socialist, cooperative or capitalist. Where the land and stocks are owned by a class of capitalists they are paying a certain wage bill per annum in terms of dollars. Dollar prices then determine the real wage rate per man year of employment and the share of gross and net profits in proceeds. The ratio of net profit in dollars to the wage bill is the ratio of exploitation. According to Sraffa, the prices of commodities are such as to make the rate of profit on the dollar value of capital uniform and constant through time, but in real life this condition is not exactly fulfilled. The rate of exploitation (with the corresponding level of the rate of profits) may, in principle, be anything between zero (which permits only enough gross profit to keep stocks intact) and the maximum which permits the labour force just to exist and reproduce itself. There does not seem to be much point in making further systematic generalisations. We have here a broad frame within which detailed studies of actual history can be carried out. This is where Sraffa leaves us and hands us over to Keynes. Notes 1 See M. Milgate "Keynes on the 'classical' theory of interest", Cambridge Journal of Economics, September 1977. 2 Preface, Production of Commodities by Means of Commodities p. v. 182