THE TOXIC ACTION OF KCN AND ITS RELATION TO 



THE STATE OF NUTRITION AND AGE OF THE 



CELL AS SHOWN BY PARAMECIUM AND 



DIDINIUM. 1 



BARBARA LEE LUND. 



INTRODUCTION. 



Many results from studies on behavior and inheritance in the 

 unicellular organisms show that the same cell is different at 

 different times. The precise conditions under which these dif- 

 ferences arise have been only incompletely determined, and in 

 relatively few instances do we know enough about the conditions 

 of their occurrence to be able to repeat exactly the results. In 

 short, physiology knows that differences of this or that kind 

 occur among cells of the same cell species (i. e., cells which are 

 apparently identical in outward appearances and history), but 

 knows very little about how they occur and what the changes 

 are in the cell that cause difference in response to identical external 

 conditions at different times. 



One of the striking instances of this variability is commonly 

 observed when individuals from a pure line of Paramecium or 

 other protozoa are taken from the same culture and placed in 

 solutions of various kinds of chemicals. Some of the cells die 

 quickly, others survive for long periods of time. What are the 

 origin and causes of such differences among individuals of a 

 pure line population? The following is an attempt to solve some 

 of the features of this problem. 2 In order to increase the general 

 significance of the results the experiments have been carried out 

 on Didinium nasutum as well as on Paramecium caudatum. 

 Preliminary experiments on Paramecium indicated that the state 

 of nutrition played an important role in determining the results, 

 so that Didinium was selected because its food (Paramecium) 



1 From the Department of Animal Biology of the University of Minnesota. 



2 For discussion of certain phases of this problem, see Jennings, " Behavior of 

 the Lower Organisms," Chap. XVI. 



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