"Marx did do original work in analyzing patterns of circular inter-dependency among industries. Such work gains few converts and is not very helpful in promoting revolution or counterreactions. But like all pioneering effort it deserves the commendation of later craftmen, and it deserves further development. There is half-truth in Schumpeter's adaption of Clemenceau: "Marxian economics is too hard to be left to the Marxians." Only half, because the present paper is seen to involve little worse than school algebra and to be well within the frontier of modern economic theory."