or piles of rubbish, i. e., obstructions when Blackstone, in the eighteenth, mentions nuisances, the cateogory has widened to include obnoxious animals, offensive trades, foul watercourses. The fundamental maxim of the nuisance law was then: "So use your own that you will not injure another." To it we have added nothing but definition of injurious acts or things. The multiplication of such acts followed the stratification of society and the division of labor. No differentiation, no nuisance, increasing differentiation, multiplication of nuisances. This is true whether we compare decade with decade, district with district, city with country, or one part of the city with another. In the so-called "slums" nothing short of an impassable or suffocating odor is considered a public nuisance, but in "resident districts" fruit stores, groceries, meat-markets, etc., apply deodorizers and purifiers constantly, and the streets are kept cleared of decomposing substances. The index at any particular time or place is the monopoly power possessed by the classes which live upon or pass over the various districts. As the term "resident district" has come to mean, not the district where the greatest number reside, but where the "best, "the moneyed, the leisure classes consume the portion of their wealth devoted to domestic display, so freedom from nuisances follows the line of income, i. e., the line of freedom from competition. If certain streets seem to disprove this statement, investigation will show that they are enjoying cleanliness, not because of demands made by tenants, but because of higher standards exacted by "up-town" people who pass frequently, or perhaps, because the "up-town" people fear the result of adjacent uncleanliness.
As the fourth period is marked by precautions against the unaesthetic or noisome, so the fifth stage develops precautions by "those who have" against the hidden dangers incident to neighboring lower standards of life, i.e., against the slum. This stage the older civilization never knew. This type of sanitation could not develop until modern industry erected rookeries, immense factories, and retail establishments, the sweat-shop, creamery, and bakery. As soon as cities were divided into dis-
