CHEM0TAX1S OF OXYTRICHA /ERUGINOSA. 293 



whether the distilled water was aerated or not. Many repetitions 

 always gave the same result. It seemed possible that here was 

 a culture with optimum alkalinity. If so an increase in its 

 alkalinity ought to produce ring formation around a drop of dis- 

 tilled water. To test this the culture was made rather strongly 

 alkaline by addition of n/100 KOH, and to a mount a drop of 

 distilled water was added. But the result was as before. In 

 every case this one race, even when the culture was made many 

 times more alkaline than in its natural state there was still a 

 purely negative reaction toward distilled water. There was evi- 

 dently an optimum condition in this culture, but it was not an 

 optimum of alkali. 



Some other cultures varied from this by showing only an 

 incipient tendency toward ring formation with distilled water, in 

 others again Oxytricha soon approached very close to the center 

 of the drop. It seems obvious therefore that various cultures 

 differ widely as to their approach to an optimum state, but that 

 this variation is not, primarily at least, correlated with alkalinity. 

 It seems plain to me, that the reactions of cultures to distilled 

 water are due not to alkalinity but to the effect of some other yet 

 unknown condition. Distilled water represents to Oxytricha not 

 merely a transition stage between weak alkali and weak acid. 

 If it did one might expect Oxytricha (always, when in culture 

 solution, negative to even very weak acid) when placed in weak 

 acid, to react positively to distilled water. A culture was made 

 acid and aerated, then a drop of distilled water introduced on a 

 mount. In some cases there was indifference, in a few there zvas 

 a positive reaction, but in by far the greatest number of cases the 

 organisms gave a negative reaction toward the distilled water, as 

 most alkaline cultures would have done, sometimes with ring 

 formation. 



The same acidified culture however reacted positively to a 

 drop of its own unacidified culture water. 



It seemed obviously desirable to find out something of this 

 unknown constituent leading to these results. Most of the 

 experiments seemed to show that such a substance was present 

 usually in more than optimum amount, hence the frequent occur- 

 rence of ring- formations around diluents. It should be noticed 



