152 



RUTH L. PHILLIPS 



the failure of this mixture to support the Ufe of Paramecium 

 during the last two months of the observations. The mean 

 division rate for C, 1.033, is somewhat lower than is characteris- 

 tic for Paramecium aurelia when living under favorable condi- 

 tions. It was therefore thought best to take the mean rate for 

 M, 1.444, as the basis for computing the various percentages. 



An examination of table 1 confirms the evidence of the pre- 

 liminary experiments, namely, that Paramecium does not or- 

 dinarily thrive upon pure cultures of bacteria. That it may 

 sometimes do so is evident from the results of feeding with the 



TABLE 1 



Summary of the results of feeding Paramecium with the bacteria, A', B', C, the 



mixtures A'B', A'C, B'C, and A'B' C , and the chance mixture M, from 



August 28, 1920, to March 7, 1921 



1 Died at end of time designated. 



2 Discontinued because unsatisfactory. 



streptothrix C. This organism was used with good effect for 

 a period covering six and one-half months. Nor should it be 

 forgotten that Paramecia from this line were doing well in pure 

 cultures of C on June 2, 1921 — a total of over nine months. 



A transitory stimulating effect on Paramecium was had by 

 combining the bacteria A' and B', as is seen by the increase in 

 division rate and percentage of high divisions and the decrease 

 in low divisions and deaths over those for these organisms when 

 fed in pure culture. That this stimulation was very fleeting is 

 evidenced by the fact that the actual duration of life of animals 

 fed upon this mixture was no longer than for those fed with A' 

 alone. 



