504 SPONTANEOUS AGGREGATION OF FLAGELLATES 



glass jars in which the Bodo swarmed, the oxygen content was con- 

 siderably lower than that in a similar vessel containing an equal 

 volume of tap water. 



A number of experiments was made to test the effects, if any, of 

 excess and of absence of dissolved oxygen on Bodo. An ordinary 

 cover-slip preparation was made and at the same time an equal 

 amount of Bodo suspension was placed on a hollow-ground slide and 

 exposed to the air in a moist chamber. 24 hours afterwards the usual 

 square-shaped band of flagellates was present under the cover-glass, 

 in the zone of optimum oxygen concentration, while on the uncovered 

 slide the flagellates were evenly distributed throughout the drop. 

 In spite of the oxygen concentration being above the optimum in the 

 second preparation, the swimming activity of the individuals was 

 alike in both. The fact that a large excess of oxygen has no effect 

 either was demonstrated at the conclusion of a gas chamber experi- 

 ment such as that described on page 492. A preparation with an 

 established Bodo band was placed in the chamber and oxygen passed 

 through the latter. The square band retired towards the center 

 becoming a ring and then a single mass in the middle after which 

 the flagellates dissipated to become evenly distributed through the 

 slide. This dissipation always occurs when the oxygen concentration 

 is more than a certain amount above the optimum; it was seen also 

 in preparations left standing for some time (page 487) . In the present 

 instance the oxygen concentration must have been very greatly above 

 the optimum since the gas chamber contained pure oxygen. The cham- 

 ber was now closed and the preparation left over night in the oxygen 

 atmosphere. 17 hours after the commencement of the experiment 

 the flagellates were swimming in full activity. The preparation was 

 then removed from the gas chamber and exposed to the air. In 3 

 hours and 10 minutes two aggregations had formed towards the center 

 and in 10 hours and 10 minutes the square band was reestablished. 

 Thus 17 hours in the presence of an oxygen concentration higher than 

 they could ever encounter in nature had no inhibitory effect on the 

 activity of the flagellates. 



To test the effect of the complete absence of oxygen an experiment 

 was devised as follows. An ordinary preparation was made of Bodo 

 suspension beneath a supported cover-slip. This was then closed 



