490 



SPONTANEOUS AGGREGATION OF FLAGELLATES 



ously to blue indigocarmine. This takes place either when the leuco- 

 base is exposed to the air or when it comes into contact with water 

 containing oxygen in solution. In our experiment under the cover- 

 glass the dissolved oxygen was abstracted from a zone of the Bodo 

 suspension bordering the drop of reduced indigocarmine. It was 

 found that all the flagellates from the neighboring region of the 

 suspension collected rapidly in this zone, forming there a crowded 

 band (Fig. 10). Thus the Bodo are attracted into a region whence 

 the dissolved oxygen has been removed. As control tests, indigo- 

 carmine alone, glucose alone, and caustic potash alone were sub- 

 stituted for the mixture of the three but in no case was there any 

 aggregation of Bodo. This experiment was repeated with precisely 

 the same result using in place of the reduced indigocarmine either 



Fig. 10. Flagellates beneath a long cover-glass attracted by an oxygen absorber 

 introduced at one end. a, oxygen absorber. 



an alkaline solution of pyrogallic acid or of hematoxylin. Both 

 of these solutions take up oxygen rapidly. In the case of the hema- 

 toxylin the best procedure was found to be to color the Bodo suspen- 

 sion lightly with the dye, which does not injure the flagellates, and 

 then to introduce some of this suspension under one end of a long, 

 supported cover-slip. Under the other end 0.1 n NaOH was let 

 in. In the zone where the two liquids meet, the hematoxylin rapidly 

 oxidizes in the presence of the alkali, abstracting oxygen from solution 

 in the water. The flagellates in the neighboring region collected in 

 a crowded band in this zone of reduced oxygen concentration. Con- 

 trols in which the alkali was replaced by water and in which the hema- 

 toxylin was omitted gave no aggregation of flagellates. 



In this way it can be demonstrated that the flagellates will collect 

 into a region where the concentration of dissolved oxygen is reduced 



