[Illustration: Cases of typhoid per 100,000 inhabitants before filtering water supply (solid) and after (shaded) in _A_, Watertown, N. Y.; _B_, Albany, N. Y.; _C_, Lawrence, Mass.; D, Cincinnati, Ohio. What is the effect of filtering the water supply?] Railroads are often responsible for carrying typhoid and spreading it. It is said that a recent outbreak of typhoid in Scranton, Pa., was due to the fact that the excreta from a typhoid patient traveling in a sleeping car was washed by rain into a reservoir near which the train was passing. Railroads are thus seen to be great open sewers. A sanitary car toilet is the only remedy. [Illustration: This chart shows that during a cholera epidemic in 1892 there were hundreds of cases of cholera in Hamburg, which used unfiltered water from the Elbe, but in adjoining Altona, where filtered water was used, the cases were very few.] [Illustration: Stone filter beds in a sewage disposal plant.] Sewage Disposal.--Sewage disposal is an important sanitary problem for any city. Some cities, like New York, pour their sewage directly into rivers which flow into the ocean. Consequently much of the liquid which bathes the shores of Manhattan Island is dilute sewage. Other cities, like Buffalo or Cleveland, send their sewage into the lakes from which they obtain their supply of drinking water. Still other cities which are on rivers are forced to dispose of their sewage in various ways. Some have a system of filter beds in which the solid wastes are acted upon by the bacteria of decay, so that they can be collected and used as fertilizer. Others precipitate or condense the solid materials in the sewage and then dispose of it. Another method is to flow the sewage over large areas of land, later using this land for the cultivation of crops. This method is used by many small European cities. [Illustration: Collecting ashes.]