PARAMECIUM IN PURE CULTURES OF BACTERIA 



433 



TABLE 2 



Growth of Paramecium caiutatum in mixed cultures of bacteria, in media of differ- 

 ent concentrations. Figures represent number of divisions. H. I., hay infusion ; 

 B. B., beef extract; ' dead, replaced from 0.025 per cent B. B.; ^ dead, replaced from 

 0.1 per cent H. I. 



Paramecium caudatum I 



0.05 per cent H. I.. 

 0.1 per cent H. I. . . 

 0.2 per cent H. I... 

 0.025 per cent B. B. 

 Filtered infusion. . . 



AVER- 

 AGE DI- 

 VISIONS 

 PER DAY 



1.000 

 1.153 

 1.077 

 1.153 

 1.000 



Paramecium caudatum II 



0.05 per cent H. I. . 

 0.1 per cent H. I. . . 

 0.2 per cent H. I. . . 

 0.025 per cent B. B. 

 Filtered infusion.. . 



0.769 

 0.922 

 0.231 

 1.153 



0.846 



and Baitsell had found a solution of beef extract to be a better 

 medium for constant use than hay infusion, we should have 

 used it here in place of the hay infusion. But the experiments 

 just recorded showed little difference for two weeks, and the 

 above mentioned workers found the beef solution superior mainly 

 when used for extended periods. Our cultures were planned to 

 cover periods of about ten days, long enough to show the effects 

 of pure cultures of bacteria on Paramecium, but not of sufficient 

 length to be affected by the constant use of the hay infusion. 



Technic devised for the growth of Paramecium in pure cultures 

 of bacteria. It has just* been stated that when the most desir- 

 able concentration of hay infusion was found (viz. 0.1 per cent, 

 which is the standard solution of Jennings, diluted ten times 

 with water) this one concentration was used for all subsequent 

 work. A supply of this medium was prepared, placed in test 

 tubes, the latter plugged with cotton and sterilized in an auto- 

 clave at a temperature of about 130''C. Sixteen lines of Para- 



THE JOURNAL OF E.XPKRIMENT.^L ZOOLOGY, VOL. 22, NO. 2 



