MENTAL EPIDEMICS 28l
the effect is not a mental unification of the two classes but a broadening and deepening of the hiatus between them. This was well exemplified in the great social storms of the Reconstruction Era in the South, and in the racial excite ments which have occurred intermittently ever since. There are, indeed, no more effective barriers to the spread of a common emotion than distinctions of class, and the effectiveness of the barriers is in direct ratio to the sharpness and fixity of these distinctions. When they become rigid and impassable as in a caste system, noth ing but a profound excitement which directly concerns some fundamental and universal human interest can give a common orientation of mind to the whole pop ulation, and then the emotion must be so intense that it suspends all the acquired controls of conduct and leaves the fundamental instincts in complete ascend ancy. What takes place then is not so much a communica tion of emotion or the radiation of an excitement from a centre, as a like instinctive reaction to a stimulus too power ful to be responded to by reason.
The third stage in social development is our modern in dustrial society. In this the caste system has dissolved or is dissolving. The hiatus between classes is no longer impass able. Families may sink from a higher into a lower, or rise from a lower into a higher, class within two generations or even one. The distinctions on the whole remain clear enough, but the lines of demarcation between the class fron tiers are almost blotted out. Even in western European countries, where the traditional aristocratic stratification of society was only less rigid than in India, the classical land of the caste, the tendency to substitute open classes for the closed-class system has profoundly modified the social organization ; while in the United States the only clearly de fined principle of stratification is income, which determines the standard of living and thus the general lines within which reciprocal social intercourse is practicable.
One might infer from this that the trend is toward the
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