FEEDING PARAMECIUM KNOWN BACTERIA 



163 



dicates that the addition of A' and B' to the chance mixture had 

 a stimulating effect. 



TABLE 4 

 Data for the growth of Paramecium, aurelia in the foods C, A' C, A' B' C, and M, 

 with the following changes in food; C, to C A', C B', C A' B'; A' C, to A' C" B' ; 

 M, to MA', MB', and MA' B', during the time from December 5, 1920, to 

 December 28, 1920 



T.\BLE 5 



Mean division rates with their probable errors, differences in mean division rates 

 with probable errors of the differences, and significance factors 

 for the data summarized 



This experiment shows that changes of the sort attempted are 

 usually accompanied by so much disturbance that no marked 



