218 



BARBARA LEE LUND. 



D 



300 



FIG. i. Paramecium. Survival time of "old" and "young" paramecia in 

 KCN. (See Table III.) Curve B represents the average survival time of "old" 

 sisters. Curve C represents the average survival time of the "young" sisters of B. 

 Curve D represents the difference between the average survival times of the'" old" 

 and "young" sisters. That is, it is the difference between the curves B and C. 

 The relatively long survival time at 30 and 40 minutes, curves A and B, is due to 

 lower temperature. 



nutrition of the cell ; for if we wished to show that it was due to 

 the bacteria serving as food it would be necessary to provide the 

 same medium (say, tap water) for both sisters, while only one 

 sister was fed with bacteria. To control the bacterial food of 

 Paramecia is very difficult, hence Didinia were used in the follow- 

 ing experiments. A pure line of Paramecia served as food for 

 the Didinia, and since the Paramecia could be washed free from 

 hay infusion and placed in tap water it was possible to have all 

 experimental conditions for the two sister cells of Didinia exactly 



