oxygen, carbon dioxide, bottom materials, plant growths, and aquatic animal 

 populations were observed and recorded. The findings of these 

 exceptionally pertinent investigations have been presented in a large 

 number of publications appearing over a period of half a century. They 

 describe changes in the aquatic biota as the pollution moved downstream and 

 also the natural purification brought about by the aquatic biota found in 

 the different areas. These studies dealt in detail with the plankton, 

 bottom organisms, and fishes, and changes in their populations over the 

 years as the organic load increased and the zones of pollution moved pro- 

 gressively downstream. Kofoid reported on "The Plankton of the Illinois 

 River 1894 to 1899" and "Microorganisms in Reservoirs and Their Relation to 

 Esthetic Qualities." Forbes and Richardson published a paper on "Studies 

 on the Biology of the Upper Illinois River" in 1913 and in 1919 another 

 paper entitled "Some Recent Changes in Illinois River Biology." In 1921 

 Richardson published a paper on "Changes in the Bottom and Shore Fauna of 

 the Middle Illinois River and Its Connecting Lakes Since 1913-1915 as a 

 Result of the Increase Southward of Sewage Pollution." In 1925 he 

 published "Changes in the Small Bottom Fauna of Peoria Lake 1920 to 1922." 

 These and many other reports on the effects of pollution in the Illinois 

 River furnish valuable data on the qualitative and quantitative composition 

 of aquatic populations in the different pollutional or life zones, their 

 value for characterizing the extent and severity of pollution, and their 

 role in natural purification. 



After the turn of the century, many pollution surveys were made by 

 state conservation or fish and game departments and state health depart- 

 ments. After the passage of the federal law of 1912, the U.S. Public 

 Health Service made a survey of the Potomac River in 1913. At the urging 

 of W.T. Sedgwick of the Massachusetts Institute of Technology, W.C. Purdy 

 entered the pollution field and served as the plankton expert for the 

 survey. He studied the biology of the river and its flats and pointed out 

 the great value of the tidal flats for the digestion and natural purifica- 

 tion of the organic wastes from the city of Washington, D.C. His findings 

 were presented in a paper entitled "Investigation of the Pollution and 

 Sanitary Condition of the Potomac Watershed." 



In 1914 Purdy was transferred to the U.S. Public Health Service Stream 

 Pollution Investigation Laboratory in Cincinnati. There he worked with the 

 bacteriologist, C.T. Butterfield, and later with the chemist, C.C. 

 Ruchhoft, who joined the laboratory staff in 1918. These three men and 

 their small staff made many valuable advances in the field of water 

 pollution research and pollution abatement. They participated in the Ohio 

 River surveys of 1914-1918 and 1937-1941, the Illinois and Scioto River 

 surveys, and the Lake Michigan survey. The results of their studies were 

 reported in a series of papers under two main headings, "Experimental 

 Studies of Natural Purification in Polluted Waters" and "Studies of Sewage 

 Purification." 



In his natural purification studies to supplement field work Purdy set 

 up a small artificial stream using one-fourth mile of eave trough. It was 

 built on the laboratory grounds on a slope to ensure the desired current. 

 Water and a sewage waste were fed in at the upper end. Pollutional or life 



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