2l6 



BARBARA LEE LUND. 



Conclusion: The older animals are evidently more resistant 

 to KCN than the younger, and the apparent exceptions shown 

 in parts I. and III. are due to the fact that the animals were 

 left to age in tap water instead of in hay infusion. This was 

 probably due to inanition and not to any deleterious effect of the 

 tap water itself. See experiment VI. below. 



TABLE II. 



SUMMARY OF RESULTS OF EXPERIMENT II., PARTS I., II., III. AND IV. 



Experiment III. In performing the preceding experiments 

 the question arose as to whether the effects of ageing in native 

 medium were cumulative; that is, whether the resistance in- 

 creased regularly as age advanced. To answer this question the 

 following experiment was performed. The procedure was the 

 same as in experiment II. except that -/V/75 KCN was used. 

 One sister was killed in this immediately after division. The 

 other sister was allowed to grow in the native medium (hay 

 infusion) and killed at ages varying from 10 to 600 minutes. 

 Thirty Paramecia were tested in each case; that is, thirty 

 "young" and thirty "old" for each time interval. Averages of 

 the survival times for the young and the old for each time 

 interval were made, and in every case the average length of life 

 after treatment with KCN was greater in the case of the old than 

 of the young animals. 



The results of this experiment are summarized by giving 

 these averages and the difference between them (Table III.). 

 They are plotted in curves (Fig. i). 



The difference between the averages increases as age of the 

 surviving sister increases. The degree of variation in survival 

 tini? is relatively small when compared to the average survival 



