172 American Fisheries Society 



ing fish on the other. In brief, Dr. Hofer's method aims 

 at the transformation of the organic but lifeless sub- 

 stances held in sewage into living organisms, the sewage 

 being thus used up in the process. Of the living product 

 the larger eats the smaller through a series of forms 

 ending in marketable food fishes. 



A brief description of the Strassburg sewage-fish 

 cultural station should begin with emphasis on its loca- 

 tion and the nature of the land put at its disposal. This 

 is of fundamental importance for the economy of the 

 experiment, which requires that such land shall be of 

 little value for other purposes, otherwise overhead 

 charges will make the business show a loss. When a 

 level tract of suitable size and small value located below 

 the sewerage system and yet high enough to turn its ef- 

 fluent conveniently into the drainage of the region, is 

 available, the first essential is complied with. 



The Strassburg plant takes a sewerage composed of all 

 the wastes of the city, domestic and industrial, besides 

 the street washings. A small portion of the total sewage 

 is diverted from the sewerage system. It is first subjected 

 to coarse filtration or screening, which frees the sewage 

 of the larger bodies floating or in suspension. This proc- 

 ess yields daily about five cubic yards of an almost 

 worthless residue. A part of the remaining sewage is 

 pumped to sedimenting tanks where it is cleared of a 

 large portion of the remaining suspended matter. The 

 sedimented matter is periodically drawn off from the 

 bottoms of these tanks to drying beds and yields a fer- 

 tilizer of some commercial value. The now partially 

 clarified sewage is ready for the fish ponds. It is, of 

 course, nearly all water — more than 99.9% of it. It still 

 contains by far the greater part of foreign matter which 

 characterized the original sewage; for two-thirds or 

 more of the solid matter in sewage is in solution. In 

 this country ordinary town sewage has at most one-tenth 

 of one per cent, of solid matter, and usually much less. 

 About half of this is inoffensive inorganic matter, of 

 which about three-quarters is dissolved. The other half 

 is vegetable and animal matter and over half of this por- 



