Discriminations between commodities, or, as they might also be called, discriminations in classification, are probably the most common of unjust railroad practices. For the purpose of establishing as near as may be uniform rules in all matters pertaining to rates, the various roads operating in a certain territory usually form traffic associations. The general freight agents of the roads that are members of the association in turn form a select body known as the rate committee. These committees of freight agents have for more than twenty years constituted the supreme authority in all matters pertaining to freight classification. The trunk line classification recognizes six regular and two special classes, and every article known to commerce is placed in one of these classes. One whom Providence has not favored with the mysterious wisdom of a general freight agent might suppose that considerations of bulk, weight, insurance and similar factors formed a basis of railroad classification. Nothing, however, is farther from the truth. Freight charges, when permitted to be fixed by railroad companies, are invariably such as the traffic will bear, and freight classifications are arranged on this principle, provided competition by water, rail or other land transportation does not demand a modification. It is, as a rule, not to the advantage of a railroad to entirely starve out any commercial or industrial concern along its line. Hence tariffs are scarcely ever made entirely prohibitory. Railroads proceed here upon the principle of the robber knight of mediæval times, who simply plundered the wayfaring trader to such an extent as to reduce his profits to a minimum. He never stripped him, for by doing so he would have prevented his return and would have destroyed his own source of revenue. In like manner a railroad will never annihilate any weak branch of business along its line, nor will it, if it is in its power, permit any business to prosper without paying to it heavy tributes out of its profits. Every commodity is therefore made to pay a transportation tax based chiefly on its value and the profit which it yields, and all classifications are prepared with this object in view.