Besides the two classes of indirect laborers here mentioned, those engaged in producing materials and those in transportation, there are several others who are paid fractions out of the bread. Subsidiary to the direct labor of the bread-maker is the labor of all those who make the instruments employed in the process (as, e.g., the oven). Materials are completely changed in character by one use, as when the coal is burned, or the flour baked into bread; while an instrument, like an oven, is capable of remaining intact throughout many operations. The producer of materials and the transporter are paid by the bread-maker in the price of his coal and flour when left at his door, so that the price of the loaf is influenced by these payments. Those persons, moreover, who, like the police and officers of our government, act to protect property and life, are also to be classed as laborers indirectly aiding in the production of the given article, bread (and by his taxes the bread-maker helps pay the wages of these officials). Shading off into a more distant, although essential, connection is another class—that of those laborers who train human beings in the branches of knowledge necessary to the attainment of proper skill in managing the processes and instruments of an industry. The acquisition of the rudiments of education, and, in many cases, the most profound knowledge of chemistry, physics and recondite studies, are essential to production; and teachers are indirect laborers in producing almost every article in the market. In this country, especially, are inventors a class of indirect laborers essential to all ultimate production as it now goes on. The improvements in the instruments of production are the results of an inventive ability which has made American machinery known all over the world. They, too, as well as the teacher, are paid (a small fraction, of course) out of the ultimate result, by an indirect path, and materially change the ease or difficulty, cheapness or dearness, of production in nearly every branch of industry. In the particular illustration given they have improved the ovens, ranges, and stoves, so that the same or better articles are produced at a less cost than formerly. All these indirect laborers receive, in the way of remuneration, a fraction, some more, some less (the farther they are removed from the direct process), of the value of the final result. § 3. Of Capital as a Requisite of Production. But another set of laborers are to be placed in distinct contrast with these, so far as the grounds on which they receive their remuneration is concerned. These are the men engaged previously in providing the subsistence, and articles by which the former classes of labor can carry on their operations.