156 



RUTH L. PHILLIPS 



M and only a single animal survived. All the Paramecia used 

 in the subsequent experiments were derived from this single 

 animal. It is interesting to note that no such period of marked 

 depression occurred later among the animals fed upon the artifi- 

 cial mixtures of bacteria, which seemed to be efficient in maintain- 

 ing the normal rhythm emphasized by Woodruff and Erdmann 

 ('14). The question immediately arises: Are we dealing in the 

 case of the artificial mixtures with a type of food, capable in 

 itself of preventing the periods of marked depression noted by 

 Calkins ('02 a), and avoided by Woodruff by the use of a 'varied 

 culture medium"? This could be determined only by attempting 

 to feed Paramecium such a mixture many months, and is a prob- 

 lem in itself. 



Since, as is indicated in table 1, the bacteria A', B' and the 

 mixture A'B' did not prove to be satisfactory as food, they have 

 not been included in the tables and graphs which follow. 



TABLE 3a 



Summary of results of feeding Paramecium aurelia in 0.1 per cent standard timothy 



hay infusion with the bacteria C, A' C, B' C, A' B' C, and M, for period I, 



from August 28, 1920, to September 28, 1920 



TABLE 3b 



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



in 0.1 per cent standard hay infusion for period II, from October 20, 1920, to 



November 24, 1920 



