154 



RUTH L. PHILLIPS 



in the mean division rates (0.0760) 9.832 times. 

 reaction may be expressed as follows : 



1.793-1.033 0.760 



— = 9.832. 



This whole 



V (0 . 0462)2 + (0 . 0824)2 0.0775 



Therefore, the increase in metabolism, as indicated by the 

 increased division rate for A'C, is significant, and demonstrates 

 that the addition of A' to C produced a food for Paramecium of 

 much greater value than C alone. The data from which the 

 significance factors were derived are given in table 2. 



TABLE 2 



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 in table 1 



When B' was combined with C, a food was obtained, which, 

 although far more satisfactory than B' in pure culture, neverthe- 

 less failed to maintain a high rate of metabolism in Paramecium. 

 This mixture w^as, therefore, discontinued after twenty-seven 

 days' trial. 



When to C were added both A' and B', a fairly satisfactory 

 food was obtained, the average daily division rate being 1.530 

 for 127 days. The significance factor for A'B'C and C is 5.758, 

 showing the mixture to be quite superior to C alone. If we 

 compare A'C and A'B'C, we find a significance factor of 2.635, 

 which indicates no real difference in the relative food values of 

 these two mixtures. Other data than division rate suggest that 

 A'C may be slightly better than A'B'C. 



The mixture M appears to be less favorable than either A'C' 

 or A'B'C, for the metabolic rate of Paramecium is lower than 



