318 ARCH E. COLE 



as food for the chironomid larvae or other organisms, which were either 

 introduced into the bottle before sealing or pumped up with the mud. 

 Bottles containing water and living organisms taken from the stag- 

 nated region which were to be used for observation in the laboratory 

 were inverted and their necks dipped in melted paraffin thus doubly 

 sealing them. 



3. Methods for observation of animals under normal conditions 



Series of samples in bottles, obtained in the manner described in 

 section 2 of this appendix were kept in an underground cellar in dark- 

 ness and at a temperature of 4.5° to 8°C. The confined organisms were 

 as near normal condition as possible and still capable of being observed. 

 The only method that could be employed of determining the habits of 

 the animals studied under normal conditions was by the observation 

 of individuals confined in the bottles containing oxygen-free water and 

 mud and kept in the manner just described. 



4. Method employed for collecting animals for experimental purposes 



Animals living in the mud at the bottom of Lake Mendota were 

 collected for experimental work by means of a mud-dredge. This 

 apparatus is similar to the Ekman ('15) dredge. It consists of a brass 

 box with movable jaws which form the bottom. These jaws are held 

 together by springs. They can be pulled up at the sides and fastened. 

 When the dredge is lowered to the bottom from the boat or from the 

 ice by means of a line, its weight carries it down into the soft mud. 

 The catch holding the jaws apart can then be released by a messenger 

 and the springs pull the jaws together, thus enclosing in the dredge a 

 quantity of the mud with the organisms living in it. The dredge is 

 drawn to the surface, its contents poured into a sieve, and the animals 

 washed free from the mud. 



5. Method for making water oxygen-free and technique for handling it 



The apparatus shown in figure 1 was constructed during the spring 

 of 1917, being completed before the writer learned of a similar appa- 

 ratus used by Pause ('18). It provided for the boiling of water until 

 all the oxygen was driven off, the presence of oxygen being detected by 

 the Winkler method. 



The apparatus consisted of a 5-liter flask (A) in which water was 

 boiled for a long period of time, thus driving off the dissolved oxygen. 

 A metal stopcock (D), which provided an opening to the flask, was 

 closed when the water stopped boiling, thus cutting off all connection 

 of the water with the outside. Nitrogen was then introduced from 

 the tank {N) through the tube /, to keep the pressure on the inside of 

 the flask, which would be lowered on cooling, equal to the atmosphere 

 pressure. The pressure on the inside was indicated b}^ the move- 

 ment of the water in the tube G. 



