This, while true as a general fact, has so many exceptions that it is not safe to trust to it. The Sanitary District Canal of Chicago has proved positively that even the most heavily germ-laden water becomes pure by running many miles at a regulated speed through the open country, but the conditions are altogether different from those of an ordinary river. First, in a river, sewage may enter at any point down-stream to add to the germs already present in the water, while nothing is allowed to enter the Drainage Canal after it leaves the city. Second, some germs live for several days and may be carried many miles. Only a microscopic test can prove whether water contains such germs. Usually such tests are not made and water is used without people knowing whether it is pure or not, but the water of the Sanitary Canal is tested at many points to determine its purity. Each hour and each mile of its journey it grows purer. This proves that although running water does purify itself, a stream that is drained into all along its course is not a fit source of water supply. Factory refuse, instead of being allowed to pollute the waters, should be turned to good use by extracting the chemicals, which form valuable by-products. All farm waste should be taken to a remote part of the farm, placed in an open shed or vat with cement floor and screened from flies to form a compost heap for fertilizers for the farm. This will amply repay the extra trouble and expense by increasing the farm crops. The sooner such refuse, especially manure, is returned to the land, the more valuable it is as a fertilizer. In cities the sewage should be disposed of in such a way as to yield a profit to the city, and also promote the health of the people. The sewage of a city of 100,000 people is supposed to be worth, in Germany, about $900,000 a year for fertilizer on account of the phosphorus it contains. The city of Berlin operates large sewage farms, using as laborers men condemned to the workhouse. The expense for land and sewer system was $13,000,000, but it pays for the money invested, with $60,000 yearly profit over all expenses. On the other hand the cost of impure water to the city of Pittsburg was reckoned at $3,850,000, and in the city of Albany, New York, the annual loss was estimated at $475,000. In the early settlement of our country all towns were built on streams, and the ones which grew and flourished were all on rivers large enough to carry commerce by boat. After the invention of steamboats, daily packet lines were run on all the principal rivers.