138 RUTH L. PHILLIPS 



A rough determination of the reaction of a watch-crystal cul- 

 ture in which Paramecium had been growing for a few days with 

 the streptothrix C as food showed an increase in alkalinity over 

 the sterile medium. Although the amount of fluid available 

 was too small to determine the exact amount of this increase, the 

 reaction obtained indicated that the presence of the organism C 

 in hay infusion tends to increase the alkalinity of the medium. 

 A similar test was made with a like amount of infusion in which 

 Paramecium was living upon the bacterial mixture, A'B'C. In 

 this case the reaction tended to be more acid than the control 

 sterile infusion. Whether this increase in acidity was due to the 

 carbon dioxide excreted by a large number of Paramecia or to the 

 reaction of the bacteria with the media or to a combination of 

 these factors, it is impossible to say. It would seem that an in- 

 vestigation of the hydrogen ion concentrations of media used for 

 cultivating Protozoa might be helpful in understanding some 

 phases of the activities of these animals. 



The fact that the hj^drogen ion concentrations of the three 

 types of media proved to be practically identical does not neces- 

 sarily indicate a similarity in chemical constitution, and it is, 

 I believe, safe to assume that they were chemically unlike. On 

 this assumption it was, therefore, possible to vary the environ- 

 ment of Paramecium by the use of these different media as well 

 as by changing the food. 



c. Isolation of the bacteria used for feeding Paramecium 



A little preliminary work demonstrated that a complete bac- 

 terial analysis of the hay infusion was impracticable in connec- 

 tion with an investigation of the reactions of Paramecium to food. 

 It was, therefore, thought best to inoculate a sterile hay infusion 

 in such a manner as to secure the types of bacteria ordinarily 

 found in the hay infusions used for growing Paramecium in the 

 laboratory. This was done with all precautions necessary to 

 exclude bacteria from sources other than hay. 



Agar plates were poured and inoculated from the infusions 

 every day for the first three days, and again at the end of nine 



