FEEDING PARAMECIUM KNOWN BACTERIA 137 



and Fray ('17) found that the high temperatures of the autoclave 

 so altered the nature of the hay infusion that Paramecium could 

 not liA'e in it. For this reason, the three-day intermittent method 

 of sterilization in the Arnold steam sterilizer has been used for 

 all media in which it was desired to grow Paramecium. This 

 method proved to be perfectly reliable. 



The different infusions were prepared as follows : 



1. The standard hay infusion of Jennings ('10) was made by 

 allowing 10 grams of chopped timothy hay to boil for ten minutes 

 in a liter of tap-water. This was cooled, brought up to volume 

 with tap-water, filtered, and then sterilized in the Arnold for three 

 successive days. From this stock infusion a 0.1 per cent solution 

 was prepared from time to time as needed. The 0.1 per cent 

 solutions w^ere sterilized in a similar manner and used as the 

 standard culture medium for inoculation wdth bacteria and for 

 growing Paramecium. 



2. An infusion was made from uncured swamp hay according 

 to the formula used for the standard hay infusion. This with 

 its 0.1 per cent solution was sterilized in the same way and put 

 aside for further use. 



3. Similarly, a third infusion was prepared from the common 

 moneywort, Lysimachia nummularia L., which had been care- 

 fully dried and used at once without further curing. 



b. Reactions of the media 



The hydrogen ion concentrations of these three infusions were 

 determined at the close of the experiments by Mr. Halstead ac- 

 cording to the Gillespie ('20) drop method. The reactions were 

 found to be as follows: For the 0.1 per cent standard timothy hay 

 infusion pH = 8.2; for the 0.1 per cent uncured swamp hay infu- 

 sion, pH = 8.2; for the 0.1 per cent moneywort infusion, pH = 8.4. 

 Since the neutral point has been determined as pH = 7, increases 

 over this point indicating alkalinity and decreases acidity, it will 

 be seen that the reactions of these media were rather markedly 

 alkaline. No attempt had been made to keep the reactions con- 

 stant by the addition of buffers, so it is impossible to say what was 

 the reaction of the media at the beginning of the work. 



