505 



at this time, either dead or alive. It was here also that the largest 

 number of septic organisms per cubic centimeter of water was ob- 

 tained July 28 to August 3, by our modification of the Kolkwitz 

 method, — 186 per centimeter, as compared with 116 at Morris and 

 15 at Marseilles. Of the pollutional species, on the other hand, there 

 were 55 per cubic centimeter at Dresden Heights as compared with 

 169 at Morris and 35 at Marseilles, while of the contaminate forms, 

 there were 90 at Dresden Heights, 76 at Morris, and 28 at Mar- 

 seilles. The mixed origin of the waters at this point was especially 

 illustrated by the further fact that clean-water species averaged 209 

 per centimeter at Dresden Heights, 287 at Morris, and 270 at ]\Iar- 

 seilles. At Dresden Heights, however, these were almost wholly 

 diatoms characteristic of Lake Michigan water, which had evidently 

 been brought down by the sanitary canal. The most significant of 

 these were two species of Tabcllaria — T. fenestrata and T. flocculosa 

 — together with Fragilaria z'iresccus and Cyclotdla kutdngiana. The 

 Tabellarias were never taken in our Illinois River plankton previous 

 to the opening of the sanitary canal, and their maximum number 

 in the Illinois in these 191 1 collections came from above Marseilles. 

 The other two species formerly occurred in both the river and lake, 

 but they were rare below Morris in July and August of 191 1 — a 

 strong indication of the Lake Michigan origin of those taken at Dres- 

 den Heights. 



The water here July zy, at a temperature of 68° F., gave us an 

 average of 13.1 per cent, of oxygen saturation as the mean of de- 

 temiinations made at 10 a. m. and i 130 p. m., the Kankakee River 

 giving us, on the other hand, just above the mouth, an average of 

 126.8 per cent, at 2 p. m., at a temperature of 71.6° F. In other 

 words, the Kankakee, supersaturated with oxygen, contained nearly 

 ten times as much as did the Des Plaines just above the junction 

 point of these two rivers. The former held in solution, on the other 

 hand, only one sixth as much carbon dioxide — 2.1 parts per million 

 to 12.8 parts in the Des Plaines. The oxygen content of the latter 

 was practically the same September 26, 191 2, as in the midsummer 

 period of the preceding year, but increased greatly in fall, reaching 

 40.3 per cent, of saturation November 14 as compared with 11.2 per 

 cent. September 26. 



Biological conditions were but little changed in 1912, as shown 

 by visits made in August and September of that year. As before, 

 no fishes were found, and no other vertebrates except a single frog. 

 ]\Iany dead shells of gastropod mollusks were seen, including Plauor- 

 bis t'riz'ok'is, Physa gyrina, and Lymncca palustris, and a single speci- 



