294 GEORGE WAGNER. 



that in spite of our knowledge of the lack of reaction of Oxytriclia 

 to carbon dioxide, I took the precaution of aerating the cultures 

 in all the above experiments, except where otherwise stated. 

 The reason for this precaution lies in the following results. 



A portion of an Oxytricha culture was taken and thoroughly 

 aerated by squirting it repeatedly into a watch glass from a 

 pipette. A mount was immediately made and a drop of non- 

 aerated liquid from the same culture introduced. The result was 

 a strong positive reaction toward this non-aerated drop. To an 

 entirely similar mount a drop of aerated culture water was added. 

 The organisms were entirely indifferent, swimming in and out of 

 the drop, with no sign of reaction. Thirdly, a non-aerated mount 

 was now made, and a drop of aerated culture water was added. 

 The drop remained free from Oxytricha, which, reacted nega- 

 tively at its outer edge. If to a non-aerated mount a non- 

 aerated drop was added, there was again indifference. These 

 experiments were repeated many times, always with the same 

 results. It is evident therefore that a non-aerated culture con- 

 tains some substance toward which Oxytricha reacts positively ) 

 and that this substance can be removed by aeration. It must 

 therefore be either volatile, gaseous or easily oxidized. 



But an aerated culture will also react negatively to hydrant 

 water or to distilled water, often with ring formation. That 

 such ring formation occurs with distilled water shows that what 

 happens here is due to another, non-volatile substance present 

 in the culture, toward which Oxytricha also reacts positively at 

 proper concentration. This second substance also seems to be 

 present usually in super-optimum amount. This second sub- 

 stance may sometimes be the alkali. That it is not always such 

 is of course well shown by the case mentioned above, where a 

 culture, after addition of much KOH and of aeration, still 

 remained purely negative to distilled water. This experiment 

 also shows that it is not merely a matter of osmotic pressure. 



An interesting experiment in this connection is that in which 

 Oxytricha, previously gathered into hydrant water by electro- 

 taxis, were mounted and a drop of slightly acidulated culture 

 water added. There was quickly formed a dense ring around 

 the drop, which was long maintained. It was evident that here 



