_Temperament and social contagion._—What lends special importance to the segregation of the poor, the vicious, the criminal, and exceptional persons generally, which is so characteristic a feature 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. It is not necessary to understand by the expression “moral region” a place or a society that is either necessarily criminal or abnormal. It is intended rather to apply to regions in which a divergent moral code prevails, because it is a region in which the people who inhabit it are dominated, as people are ordinarily not dominated, by a taste or by a passion or by some interest which has its roots directly in the original nature of the individual. It may be an art, like music, or a sport, like horse-racing. Such a region would differ from other social groups by the fact that its interests are more immediate and more fundamental. For this reason its differences are likely to be due to moral, rather than intellectual, isolation. 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 human 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 conveniently and profitably studied. ROBERT E. PARK. CHAPTER II THE GROWTH OF THE CITY: AN INTRODUCTION TO A RESEARCH PROJECT