§ 7. The growing interdependency of trades and markets, the ever closer sympathy which exists between them, the increased rapidity with which a movement affecting one communicates itself to others, is another striking characteristic of modern trade. This interdependency is in large measure one of growing structural attachment between trades and markets formerly in faint and distant sympathetic relationship. Formerly, agriculture was the one important foundational industry, and from the feebleness of the transport system the vital connections and the unity it supplied was local rather than national or international. Now the agricultural industries no longer occupy this position of prominence. The coal and iron industries engaged in furnishing the raw material of machinery and steam-motor, the machine manufacture, and the transport services, are the common feeders and regulators of all industries, including that of agriculture. They form a system corresponding to the alimentary system of the human body, any quickening or slackening of whose functional activities is directly and speedily communicated to the several parts. Any disturbance of price, of efficiency, or regularity of production in these foundational industries is reflected at once and automatically in the several industries which are engaged in the production and distribution of the several commodities. The mining and metal industries, shipbuilding, and the railway services are recognised more and more as furnishing the true measure and test of modern trade; their labour enters in ever larger proportion into the production of all the consumptive goods. Besides the general integration or unification of industry implied by the common dependency of the specific trades upon these great industries, there are other forces engaged in integrating groups of trades. Foremost is the "roundabout" method of production, to which our attention has been already directed. Not merely does this capitalist system bring a number of trades and processes under the control of a single capital, as a single complex business, but it establishes close identity of trade-life and interests among businesses, trades, and markets which remain distinct so far as ownership and management are concerned. § 8. If we take the mass of capital and labour composing one of our staple productive industries, we shall find that it is related in four different ways to a number of other industries.