IRRIGATION AND SEWAGE FARMS 143 



;rops or the purification of the sewage. The lowest of these 

 figures is equal to 20,000 gallons per acre per twenty-four hours ; 

 the Berlin farms (see table) only take 2,730. It must be 

 remembered that in cases where such large quantities are sup- 

 plied frequently after a time the land becomes " sick," and 

 great nuisance has been occasioned. 



During igoo the Gennevilliers farm of goo hectares received 

 54,223,620 cubic metres of sewage, equal to about 14,500 gallons 

 per acre per twenty-four hours. On a report of M. Launay, 

 who is known as an advocate of the tout a Pegout system, it has 

 been decided to experiment with the English bacterial methods 

 on the Paris sewage, which is organically stronger than the 

 average met with in England. At the same time it is con- 

 templated to extend the irrigation area. *' Intensive irrigation " 

 has been tried with rather satisfactory results at Gennevilliers, 

 and later at Acheres. Instead of supplying the land with the 

 amount of water requisite for culture, the amount was increased 

 ten and twelve times, accompanied with successive ploughings 

 whenever the superficial soil became caked with an impermeable 

 layer of mud. Not only did the soil retain its filtering proper- 

 ties, but also all the decomposing substances were completely 

 absorbed and assimilated without the aid of any vegetation. 



At Milan the sewers join in a canal, the Vettabia, which dis- 

 charges into about 4,000 acres of land arranged in terraces, the 

 final effluent falling into the river about ten miles below the 

 jcity. The proportion of sewage applied is calculated as that of 



)rty persons per acre of land. 



At Dantzig, Breslau, and other places on the Continent, 

 sewage farms are also at work, but almost invariably on light 



50il. 



2. Catchwater, — On irregular ground an upper main carrier 

 is made i to 2 feet wide and 6 to 10 inches deep. The sewage 

 )verflows from it at any point by temporarily damming, and, 

 Lfter spreading over the ground, the excess collects in a lower 

 :atchwater gutter made to the contour of the land, from which 

 "it is dammed and released on the same principle. This method 

 requires much control. 



Growing plants, especially of certain species, are capable to 

 a certain extent of absorbing and using as food the organic and 

 ammoniacal constituents of raw sewage, and, by means of 

 the numerous enzymes they secrete, are able to dissolve and 

 utilize organic suspended matter. But vegetation ordinarily 



