2. _The efficiency of labor is limited objectively by the abundance and quality of material resources._ Material resources include both those called natural (as the field and its fertile qualities), and those called artificial (as improvements and machinery). According as these resources are more or less developed, as labor is employed in a fertile or a barren field, with a sharp tool or a dull one, with a highly developed machine or a poor one, the product is more or less. If resources were much more abundant than at present, many goods now scarce would become almost, or quite, free. In the last chapter it was shown that an increase of the labor in a limited area or with a limited supply of indirect agents results in a decline in the relative bounty of the environment. A certain part of the result is thought of as due to material agents, a certain part to labor. "Efficiency of labor" is thought of in the narrower sense as the part of the product that is logically attributable to labor,--the laborer's contribution to the value of the product,--as apart from rent, the part attributable to material resources. [Sidenote: Causal relation of wages and efficiency; food] 3. _The laborer's efficiency is greatly affected by the quality of his food, clothing, and shelter._ Usually workmen that are getting good wages enjoy abundant food and creature comforts; poorly paid workers go scantily fed. The question arises: which is cause, which effect? Some maintain that all that is needed to make workmen more efficient is to feed them well. In some cases this is probably true. The Porto Ricans enlisted in the American regular army are reported to have increased at once in strength, weight, and vigor; the Filipino recruits, thanks to the American army rations, soon outgrew their uniforms. Some employers in Europe pay their workmen an extra sum on condition that it is spent for meat. But if wages increase, it is by no means certain that more or better food will be bought or if it is that the workmen's powers will be increased. There is a limit to the benefits of increasing food. There is some reason to believe that in America great numbers of our people, perhaps even many manual laborers, would be better off if they bought simpler and less costly food. The maximum of health and vigor may be attained with moderate outlay, and beyond that point richer food doubtless does more harm than good. Poor judgment in the selection of food is shown in many workers' families, and there is no appreciation of its influence on health. [Sidenote: An experiment in feeding]