There are a number of studies of cities as cultural centers. The city of Moscow has often been described as the city of churches, for instance, and as such has exercised an influence over the life of Russia all out of proportion to its function in other respects. Similar studies are available of Rome, Venice, Dresden, and a number of others. 6. With the advent of modern methods of communication the whole world has been transformed into a single mechanism of which a country or a city is merely an integral part. The specialization of function, which has been a concomitant of city growth, has created a state of interdependence of world-wide proportions. Fluctuations in the price of wheat on the Chicago Grain Exchange reverberate to the remotest part of the globe, and a new invention anywhere will soon have to be reckoned with at points far from its origin. The city has become a highly sensitive unit in this complex mechanism, and in turn acts as a transmitter of such stimulation as it receives to a local area. This is as true of economic and political as it is of social and intellectual life. Baer, M. _Der internationale Mädchenhandel_, Vol. XXXVII in “Grossstadt Dokumente” (Berlin, 1905). Shows that the large city is the center of the world white-slave traffic. (III, 4; VII, 5; IX, 4.) Bernhard, Georg. _Berliner Banken_, Vol. VIII in “Grossstadt Dokumente” (Berlin, 1905). While primarily a study of Berlin banks, shows the large city as the center of the economic life of the world. (III, 4; V, 1; IX, 1, 4.) Jefferson, Mark. “Distribution of British Cities and the Empire,” _Geog. Rev._, IV (November, 1917), 387–94. “English cities are unique in that they have taken the whole world for their countryside.... The conception of the British empire as the direct result of English trade in English manufactures, which in turn are largely a response to English treasures in coal and iron, is strongly reenforced by the distribution of her great cities.” (III, 4; VI, 8.) Olden, Balder. _Der Hamburger Hafen_, Vol. XLVI in “Grossstadt Dokumente” (Berlin, 1905). The influence of world-commerce on the city. (III, 3, 4; IV, 4; V, 1; IX, 1, 4.) Penck, Albrecht. _Der Hafen von New York_, Vol. IV of the collection, “Meereskunde” (Berlin, 1910). An excellent view of the traffic in the harbor of New York. (III, 2, 3, 4.) Zimmern, Helen. _Hansa Towns_ (New York, 1895). An historical example of a typical function of cities in world-economy. (I, 2; II, 2.) V. THE ECOLOGICAL ORGANIZATION OF THE CITY