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612 of city life, is the fact that social contagion tends to stimulate in divergent types the common temperamental differences, and to suppress characters which unite them with the normal types about them. Association with others of their own ilk provides also not merely a stimulus, but a moral support for the traits they have in common which they would not find in a less select society. In the great city the poor, the vicious, and the delinquent, crushed together in an unhealthful and contagious intimacy, breed in and in, soul and body, so that it has often occurred to me that those long genealogies of the Jukes and the Tribes of Ishmael would not show such a persistent and distressing uniformity of vice, crime, and poverty unless they were peculiarly fit for the environment in which they are condemned to exist.

We must then accept these "moral regions" and the more or less eccentric and exceptional people who inhabit them, in a sense, at least, as part of the natural if not the normal life of a city.

Because of the opportunity it offers, particularly to the exceptional and abnormal types of man, a great city tends to spread out and lay bare to the public view in a massive manner all the characters and traits which are ordinarily obscured and suppressed in smaller communities. The city, in short, shows the good and evil in human nature in excess. It is this fact, perhaps, more than any other which justifies the view that would make of the city a laboratory or clinic in which human nature and social processes may be most conveniently and profitably studied.