214 



BARBARA LEE LUND. 



TABLE I. 



Several hundred paramecia were transferred from a pure line mass culture to 

 each of two jars of tap water, and about twenty of these animals were taken at 

 random each day and treated with KCN. The averages of these survival times is 

 given in the vertical column headed "Average survival time in minutes." The 

 average of the survival times of 43 control individuals from the hay infusion was 

 2.19 minutes. 



point which is the most constant should be used. I obtained 

 dividing animals in the usual way (described below) and used 

 the daughter cells as soon as division had taken place. Thus 

 the animals were all the same age. The two sisters were placed 

 in a watch crystal with I c.c. .W/75 KCN solution, and the time 

 of cessation of movement recorded. They were further watched 

 and the time of beginning cytolysis recorded. Two experiments 

 were carried out, 30 animals being tested in the first and 60 in 

 the second. In order to obviate giving all the detailed data 

 the standard deviation, which is a measure of the degree of 

 variation, is given. In the first experiment the standard devia- 

 tion for the cessation of movement was found to be 2.74 .23, 

 while for cytolysis it was 3.86 .33. In the second the figures 

 were 1.08 .06 for cessation of movement, and 2.37 .13 for 

 cytolysis. Thus it is seen that the time of cessation of movement 

 in KCN is less variable, and throughout this work I have used 

 it as the "death point." 



Experiment II. Since the animals in experiment I. were 

 taken at random from a pure line mass culture it is apparent that 

 (i) some of them must have been old and some of them young; 



