182 RUTH L. PHILLIPS 



a long period of time. These two artificial mixtures were nearly 

 as satisfactory as the usual chance mixture. 



When Paramecia are fed with known mixtures of bacteria, it 

 is found that minor fluctuations in division rate occur which are 

 independent of endomixis, and like it do not seem to be greatly 

 influenced by environment. The evidence gathered tends to 

 favor constancy of food rather than frequent change. The in- 

 fluence of ordinary media is practically without effect. Para- 

 mecium is unable to utilize food substance dissolved in such 

 media. 



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