History of Sanitation

110 HISTORY OF SANITATION Boundary line indicated by line of dashes. Cases of cholera by solid circles. Cases of cholera imported from Hamburg by circles. Water mains in Hamburg streets by black lines. city of Hamburg, a free German city, with a population of 640,400, is derived from the Elbe above where the sewage is discharged into the river but not sufficiently far away to escape contamination from a recision of polluted water at flood tide. This water after some imperfect sedimentation passes direct to the consumer without filtration. The supply of water to Wandsbeck, a city of 20,000 popula- tion, is obtained from a lake which is unexposed to contamination and is filtered before being delivered to the mains. The supply to Altona, on the other hand, a Prussian city of 143,000 inhabi- tants, is obtained from the river Elbe at a point about 8 miles below where itreceives the com- bined sewage of the three cities, with their popu- lation of over 800,000. It will thus be seen that the source of sup- ply to Altona is the worst of the three. This most grossly polluted supply, however, is filtered with exceeding care before delivery to the consumers, and to this fact is attrib- uted the freedom from cholera that visited Hamburg in