"I think you will find it a very obvious one upon reflection," replied the doctor. "Under private capitalism, you see, there was no public or governmental system for organizing productive effort and distributing its results. There was no general and unfailing machinery for bringing producers and consumers together. Everybody had to seek his own occupation and maintenance on his own account, and success depended on his finding an opportunity to exchange his labor or possessions for the possessions or labor of others. For this purpose the best place, of course, was where there were many people who likewise wanted to buy or sell their labor or goods. Consequently, when, owing either to accident or calculation, a mass of people were drawn together, others flocked to them, for every such aggregation made a market place where, owing simply to the number of persons desiring to buy and sell, better opportunities for exchange were to be found than where fewer people were, and the greater the number of people the larger and better the facilities for exchange. The city having thus taken a start, the larger it became, the faster it was likely to grow by the same logic that accounted for its first rise. The laborer went there to find the largest and steadiest market for his muscle, and the capitalist--who, being a conductor of production, desired the largest and steadiest labor market--went there also. The capitalist trader went there to find the greatest group of consumers of his goods within least space. "Although at first the cities rose and grew, mainly because of the facilities for exchange among their own citizens, yet presently the result of the superior organization of exchange facilities made them centers of exchange for the produce of the surrounding country. In this way those who lived in the cities had not only great opportunities to grow rich by supplying the needs of the dense resident population, but were able also to levy a tribute upon the products of the people in the country round about by compelling those products to pass through their hands on the way to the consumers, even though the consumers, like the producers, lived in the country, and might be next door neighbors. "In due course," pursued the doctor, "this concentration of material wealth in the cities led to a concentration there of all the superior, the refined, the pleasant, and the luxurious ministrations of life. Not only did the manual laborers flock to the cities as the market where they could best exchange their labor for the money of the capitalists, but the professional and learned class resorted thither for the same purpose. The lawyers, the pedagogues, the doctors, the rhetoricians, and men of special skill in every branch, went there as the best place to find the richest and most numerous employers of their talents, and to make their careers.