The homogeneous labor force (which we have assumed temporarily) will distribute itself among all the various industries in society in proportions determined by the marginal product in each industry. Capital will also distribute itself throughout the system of industries, tending, of course, in the long run, to appear in each industry in such proportions as will, apart from inequalities of risk, produce everywhere an equality of its returns. Assuming the distribution of capital to have reached a condition of equilibrium—it being no part of our present task to follow out a theory of interest—let us try to show that labor will distribute itself over the field of industry in such a manner that exchange values will be proportionate to marginal labor costs. If labor flows from one industry to another, the total output of the first industry will decline and that of the second will increase. The change in the supplies of the respective products of these industries will alter the exchange values of these articles. Different distributions of labor among industries will give rise to different relative supplies of commodities and different exchange values. As the supply of labor in any industry increases, its marginal product decreases. If all occupations possessed the same disutility, the supply of labor would be so distributed that its marginal product would have the same exchange value in all industries. But if some occupations necessitate higher disutility costs than ordinary, the supply of labor obtainable for those industries will decrease until the exchange value of the marginal product is raised till it compensates for the superior disutility.[263] If one commodity is produced at a higher disutility cost (to the labor directly employed upon it) than another, the marginal product of labor in it will have a higher exchange value. If 6 A in one industry and 1 B in another make the marginal product of a labor-day, 6 A will exchange for 1 B, provided the disutility of labor is the same in both employments. But if it costs more disutility to produce 6 A than 1 B, the relative supplies of A’s and B’s would be so adjusted that 6 A will exchange for more than 1 B. Thus a superior disutility cost raises the exchange value of a commodity, in order that this commodity may afford a superior value product to labor. Labor-power is a peculiar production good. Like other production goods of manifold productive uses, its expenditure constitutes potentiality cost; but it is unlike others in that human pain cost is an ever-present incident to its expenditure. The distribution of labor power among different productive uses is not governed solely with reference to its share of value derived from the product, but is governed in part with reference to the pain-cost involved in the production of the product. A higher disutility necessitates a higher share of exchange value. Thus it comes to pass that this most disposable and important of production