292 GEORGE WAGNER. 



When similarly aerated cultures are tested with alkaline solu- 

 tions it is found that with very weak alkalies, such as nj 1,000 

 — nj 1, 500 KOH, the results were quite parallel with those with 

 distilled water. That is, there was a ring-like aggregation around 

 the edge of the drop. When the culture was made slightly acid, 

 and then a drop of hydrant water (alkaline) was introduced, there 

 was usually a more or less distinct ring formation, occasionally a 

 complete negative reaction. The hydrant water used was decid- 

 edly more alkaline than the ordinary cultures of Oxytricha. 

 That Oxytricha forms a ring around such a drop, might make 

 one suppose that here we find an optimum of slight alkalinity for 

 Oxytricha. But such proves not to be the case, at least not in 

 sO simple a form. Many experiments showed that so far as my 

 cultures went, Oxytricha was always negative to stronger KOH 

 (72/200) often with formation of a ring, and without exception 

 wholly indifferent to weaker KOH. There was never a gather- 

 ing within the drop no matter what dilution was used. 



It seems then that there is really no optimum strength of 

 alkali in which Oxytricha will gather. In those cases, just men- 

 tioned, where there is a ring formed, we must rather suppose 

 that the alkali plays no part except to repel, but that the water 

 acts as diluent to some other substance present in the culture, 

 attractive to Oxytricha, but present in super-optimum amount. 



In cultures made slightly acid, OxytricJia reacts to weak alkali 

 either by collecting in it (rarely), or by forming a ring around it, 

 depending on the strength of the alkali. Here again it is prob- 

 ably not an optimum condition somewhere in the alkali that 

 causes the result, but rather a reduction to an optimum amount 

 of some other substance present in the culture medium, coupled 

 with a strongly negative reaction toward the acid. For if instead 

 of a weak alkali we use a drop of culture liquid, which is nor- 

 mally weakly alkaline, we find an immediate and strong positive 

 reaction in all cases. It is then not alkalinity but an unknown 

 factor that produces this result. That alkalinity is not the factor 

 is shown by further experiment. 



In one culture it was found that Oxytricha when exposed in 

 culture water to a drop of distilled water reacted purely nega- 

 tively, and this whether the culture was aerated or not, or 



