502 SPONTANEOUS AGGREGATION OF FLAGELLATES 



I have found that both the experimental data of these workers are 

 correct, but that nevertheless they do not lead to their conclusion. 

 I tried the effect of mineral acids on Bodo by letting the acid in under 

 one end of a long, supported cover-slip, under which some Bodo 

 suspension had just previously been introduced. In a zone parallel 

 to the junction of the two liquids a band of flagellates rapidly accumu- 

 lated. A series of such tests was made with acids of decreasing 

 strengths and it was found that the reaction became feebler each time 

 until a point was reached (at 0.0005 n HCl) when the Bodo no longer 

 reacted to the acid at all. Nevertheless 0.0005 n HCl, tested with 

 Congo red as indicator, is a considerably stronger acid than a saturated 

 solution of CO2 in water. Congo red is turned violet by 0.0005 n 

 HCl whereas the scarlet color of this indicator in distilled water takes 

 on a very slight bluish tinge only when the solution is saturated with 

 CO2. 



Further it has already been shown (page 489) that the flagellates 

 do not collect in the region next a drop of water saturated with CO2 

 let in under the cover-slip. Jennings and Moore made no attempt 

 to determine quantitatively the exact strength of acid solution to which 

 these organisms react. In fact, we are dealing here with a phenom- 

 enon quite unconnected with spontaneous aggregation, a reaction 

 of the flagellates to acids and the weakest effective acid is stronger 

 than carbonic acid. 



It is worthy of remark that the accumulation of a crowded zone of 

 Bodo in the region in front of an acid introduced beneath the cover- 

 slip is much more marked in aerated than in non-aerated suspensions, 

 which is the reverse of the reaction of the flagellates to a region of 

 reduced oxygen concentration. Indeed an acid as weak as 0.001 N 

 HCl produces a slight collection in an aerated preparation only and 

 none in one made by taking liquid straight from the Bodo culture 

 jar. The crowded zone next the acid always dissipates before the 

 subsequent commencement of aggregation and band formation of the 

 flagellates in the region of low oxygen concentration. 



With regard to the gas bubbles, it is true that flagellates collect 

 around a carbon dioxide bubble and not around an air bubble, but 

 it is equally true that flagellates collect around a hydrogen bubble. 

 Jennings and Moore did not try the hydrogen bubble. It is evidently 



