222 



BARBARA LEE LUND. 



TABLE V. 



Didinium. 



D. Time after division at which the sisters, both of which had been subjected 

 to the same treatment, were killed. 



B. Each number represents the average survival time of 30 Didinia. 



C. .Each number represents the average survival time of the 30 sisters of the 

 corresponding set of row B. 



A. Differences between B and C. 



Two other experiments on Didinium were carried out which 

 were duplicates of experiment IV., except that saponin was used 

 in one case and phenylurethane in the other, in place of KCN. 

 The survival time varied with individuals apparently irrespective 

 of the state of nutrition of the cell. The death points were less 

 definite than in the case of KCN, and hence further efforts to 

 trace the causes of difference in survival time in these substances 

 was abandoned for the time being. 



Some time after the preceding results were obtained it was 

 found possible to grow pure lines of Paramecia in tap water by 

 feeding them yeast, thereby making it possible to duplicate 

 experiments IV. and V. on Didinium. 



Experiment VI. A pure line of Paramecia was raised in a 

 suspension of fresh yeast and tap water. The Paramecia were 

 centrifuged and washed thoroughly every morning, and added 

 to a new suspension of fresh yeast to continue the culture. The 

 cultures were kept in Syracuse watch glasses. If a culture is 

 neglected and bacteria develop to any extent, the Paramecia 

 become abnormal and finally die. If a starved Paramecium. is 

 put into a freshly made yeast suspension it eats greedily, and in 

 a few hours increases greatly in size. From such yeast fed 

 material, animals with constrictions were picked out with a 



