339 



191 T, and 1918 the weekly rale of killings ran for weeks at a time at 

 more than double the average weekly rate of 1914; and in November 

 and December, 1918, particularly, at rates representing increases of 110 

 to 145 per cent over the average weekly rate five years earlier. These 

 weekly peaks were in the late fall or early winter, when it is presumed 

 that a large portion of the wastes would settle to the bottom, not far 

 away from their source, ready to be washed out, still to a considerable 

 extent undecomposed, with the first heavy rains of spring. 



Heavy mortality among the snails was noted at points all the way 

 from Spring Valley to Havana during and following summer floods 

 in 1917. In August of that year dead snails acres in extent were seen 

 floating down the Illinois past Peoria and Havana ; and in places 

 were from one to two feet deep along the water-front at Peoria. 

 In late summer 1918, while in the field with chemists of the State 

 Water Survey, it was noted that all snails except one species of Mus- 

 culium and one Campeloma of imusual hardiness seemed already to 

 have been killed both at Lacon and Chillicothe. During the five weeks 

 July 22 to August 31 that year we got our first records of surface 

 dissolved oxygen under one part per million south of Spring Valley — 

 finding them then extending as far sputh as Lacon*. 



After 1918, up to the end of 1921, there was a long-sustained re- 

 cession in the packing industry, which carried the slaughtering figures 

 off more than a billion and a third pounds from the 1918 peak, or to 

 wifhin 443 million pounds of the 1914 rate (only 14.5 per cent above 

 the 1914 figure). 



Between 1921 and 1928 the slaughtering rate moved up 400 mil- 

 lion pounds to a year total for 1922 of 3,975 million, and this was ac- 

 complished without seeming to exert any further seriously unfavorable 

 influence on chemical or biological conditions ; except as it was possibly 

 reflected in increase in numbers of the sludge or nuid worms (Tubi- 

 ficidae). 



The present paper compares the condition of the bottom fauna of 

 Peoria Lake as found in July-September, 1922, with that of the sum- 

 mer of 1920, which was probably very close to its point of low condi- 

 tion following the mortality of 1917-1918, just referred to; with the 

 result, in general, of indicating an essentially slight though measurable 

 improvement in the two years. 



•Third Annual Report. State Dlv. Waterways, 1919-19:'li. pp. 28-32. 



