502 



parts per million, February 17 of the same year. At the tempera- 

 tures of the time, the first of these ratios was equivalent to 3.5 per 

 cent, of oxygen saturation, and the last to 64.9 per cent. The aver- 

 age of the six observations made, was 4 parts of oxygen per million, 

 or 31.9 per cent, of saturation. The general conditions were thus 

 those of lake water rather heavily loaded with organic debris which 

 had not yet undergone any great degree of putrefaction. 



Plants and Animals. — Consistently with this statement, in Sep- 

 tember, 191 T, a few small shiners (Notropis athcrinoidcs) one to 

 two inches long, were alive in the water, although in a dying state; 

 but all the larger minnows of this species, together with many spot- 

 tailed minnows {N. hudsonius), silvery minnows (HybogiiatJius 

 michalis), and lake perch, were stranded, dead, along the shores. In 

 the cooler weather of November, 191 1, a larger proportion of the 

 shiners were alive, and a single large fish, possibly a carp, was in- 

 distinctly seen moving away from the riprap at the north shore. All 

 the fishes found, were common Lake Michigan species. A single 

 frog was the only other vertebrate taken. 



A cursory examination of the bottom sludge November i, 191 1, 

 showed no signs of animal life; and the only insects seen in or on 

 the water were a back-swimmer (N^otonccta) and several water- 

 boatmen (Corixa), both of which, as they breathe air, can afiford to 

 be indifferent to a deficiency of dissolved oxygen. No snails or crus- 

 taceans were found in the water at this place in either year. Along 

 the riprap at the edge of the canal in 19 12 was a mixture of normal 

 and septic species of alg^e, with others representing medium stages 

 of contamination. The most abundant clean-water species were 

 Ulothrix zonata and Schizonicris Iciblcinii, barely submerged on the 

 riprap, where they were mixed with Oscillatoria liniosa, to be classed 

 as a contaminate species. There were occasional slight traces of 

 Sphccrotilus natans and Bcggiatoa alba, both highly distinctive of 

 septic or polluted waters, together with considerable growths of 

 Stigcocloninin tcnuc (a contaminate form) and Chlorclla vulgaris, 

 the latter encrusting stones. Among the meshes of the marginal 

 algae were many septic Protozoa and rotifers (Bodo saltans, Vorti- 

 cella rnicrostonia, and Rotifer acti}innts), together with others com- 

 mon in polluted waters {Oikonionas ternio, Monas vivipara, and 

 AntJiopJiysa zcgctans). 



Des Plaines River, Lockport 



September, iqii. — In late September of 191 1 the Des Plaines at 

 Lockport was much more offensi\'e than the sanitarv canal, its 



