TOXIC ACTION OF KCN ON PARAMECIUM AND DIDINIUM. 221 



the average survival times of each and the differences between 



these averages. The difference is also plotted in Fig. 2, curve A. 



These results demonstrate that in the same environment the 



differences in survival time of the sisters do not increase but 



FIG. 2. Didininm. Survival time of Didinia in KCN. Summary of Tables 

 IV. and V. The abscissa represents time in hours between division and death of 

 Didinia. The ordinate represents survival time in minutes. Curve C represents 

 the average survival time of fed Didinia. (See Table IV, C.) Curve represents 

 the average survival time of the starved sisters of C. (See Table IV., E.) Curve 

 D represents the difference between the average survival times of fed and starved 

 sisters. That is, it is the difference between C and E. (See Table IV., D.) Curve 

 A represents the difference between the average survival times of the less and more 

 resistant sisters, when both are starved. (See Table V., A.) 



if anything decrease with time; i. e., the cells tend to become 

 more alike in their resistance to KCN, and therefore the large 

 difference shown in experiment IV. must be due to the food 

 one has eaten while the other has starved. Table V. shows that 

 the difference in survival time at one half and one hour is greater 

 than at any subsequent time. This is explained by the fact that 

 division in Didinium is often unequal, one sister evidently con- 

 taining more food in vacuoles than the other. As this food is 

 used up by the cell the difference in survival time becomes less. 

 (See experiment VI. below.) 



