io6 



E. J. LUND. 



means of the hook and wire. The stender dish, Fig. i, d, may 

 either be suspended as shown or held rigidly by an appropriately 

 shaped clamp of wire fixed to the stopper with cement. 



The procedure in brief is as follows: One to five cubic centi- 

 meters of a suspension of Parawecium which have previously 

 been gradually transferred to pure tap water from native hay 

 infusion are placed in the dish, Fig. I, d. Ten or fifteen cubic 

 centimeters of the w/ioo Ba(OH) 2 solution are run into the bottle 



c 



FIG. i. 



through a small hole in a cardboard disk which is placed over 

 the mouth of the bottle shown in the photograph. The dish is 

 then placed on the hook of the stopper and the bottle quickly 

 stoppered as shown in Fig. i. The ground glass stopper should 

 be slightly greased and the bottle tightly stoppered. The CO 2 

 already in the air in the bottle and the CO 2 given off from the 

 organisms in the suspended dish diffuses into the Ba(OH)2 

 solution and quickly forms the insoluble white precipitate of 

 BaCOs. This absorption continues until no more Ba(OH)2 

 remains if sufficient CO 2 is produced to neutralize all the free 

 base, for the BaCOs is practically insoluble and hence the reac- 

 tion goes practically to completion. At the end of the desired 

 period, the length of which is determined by the rate of CO 2 pro- 

 duction by the organisms and conditions of the experiment, the 

 stopper is quickly removed and the bottle is again covered with 



