SoME PRELIMINARY OBSERVATIONS ON THE OXYGENLESS 
REGION oF CENTER LAKE, Kosciusko Co., IND. 
HERBERT GLENN IMEL. 
It has been found that some of our lakes contain no free oxygen during 
the summer months. 
Birge and Juday (’11) found that Beasley and Mendota Lakes not only 
had such oxygenless regions but that animal life existed in these regions. 
They report sixteen genera of living, active protozoa, three of worms, two 
rotifers, two crustacea and one mollusc. 
Seott found in his studies of lakes of northern Indiana that Center Lake, 
Kosciusko county, had such a region, and under his direction the writer 
undertook, during the summer of 1915 to find out what forms of animal 
and plant life existed in this region. 
According to Birge and Juday (11), after the autumnal overturn, during 
the winter, and until the approach of spring, the gas conditions are very 
nearly uniform throughout the lake, but with the approach of spring, and 
through the spring and summer, the oxygen content becomes less and less 
in the lower strata while the carbon dioxide, both free and fixed, becomes 
greater and greater until by July 15 or August 1, the free oxygen is zero 
while the carbon dioxide is very great. (See Figs. 6, 7, 8.) 
This condition is brought about in three ways: (1) by the respiration 
of the plants and animals in it; (2) lack of surface contact with the air; 
(3) decomposition of the dead organisms in it. 
Determinations of the temperature, free oxygen, free and fixed carbon 
dioxide, were made at the beginning and the end of the observation period, 
July 28 and August 26. The oxygen was determined by the Winkler 
method and the temperature was read by means of a thermophone. The 
results of these readings are shown on graphs attached hereto. (See 
Fig. 5.) 
A pump, with a hose marked off in meters, was used in the collection 
of the water. The samples of plankton were collected by pumping a quantity 
of water through a plankton net at the desired depth and then rinsing off 
with the last stroke into a collecting bottle. This method was used for 
