FEEDING PARAMECIUM KNOWN BACTERIA 143 



Lactose bouillon: no acid, no gas, red growth at top. 



Saccharose bouillon: no acid, no gas, red growth at top, 



Mannite bouillon: no acid, no gas, red growth at top and red sedi- 

 ment. 



Organism C. A streptothrix belonging to group II, Streptothrix 

 of Chester. Isolated from a nine- to fourteen-day hay infusion. 



Morphology: long filaments, fruiting bodies produced by multiple 

 division of a filament, unbranched. 



Agar colonies: myceloid, aerial hyphae formed, edge not well- 

 defined, growth rather slow, chromogenic, shell pink, color easily lost. 



Staining reactions: Gram negative. 



Gelatin: liquefies very slowly, becoming evident after two months, 

 growth slow over top and along line of stab where it is villous with 

 radiatingly extending processes. 



Litmus milk: alkaline and slowly peptonizing. 



Bouillon: growth flaky. 



Dextrose bouillon: no acid, no gas, membrane at top which drops 

 to bottom if shaken, flocculent sediment. 



Lactose bouillon: no acid, no gas, growth granular with round 

 colonies gathered at top. 



Saccharose bouillon: no acid, no gas, growth granular with round 

 colonies gathered at top. 



Mannite bouillon: no acid, no gas at first, but showing tendency to 

 gas formation beneath the membrane which forms at the top. 



Organism J'. B. coli. Isolated from a laboratory stock culture. 



Organism K' . B. cereus. Isolated from a laboratory stock culture. 



Organism L'. B, proteus. Isolated from a laboratory stock culture., 



e. Method used for growing Paramecium in pure cultures of 



bacteria 



It is obvious that if we are to cultivate Paramecium in pure 

 cultures of bacteria, the animals must first be rendered bacteria- 

 free, and the cultures must be so handled as to exclude contami- 

 nation with foreign bacteria throughout the course of the experi- 

 ments, Hargitt and Fray ('17) devised a method for freeing 

 Paramecium of bacteria by washing the animals individually 

 with sterile water in depression slides placed in Petri dishes. The 

 Petri dishes also served as moist chambers in which the animals 

 could be grown and observed without danger of contamination. 

 Their results show that depression sUdes are better than ordinary 

 watch-crj^stals for washing, and that they could rely upon five 

 successive washings for sterilizing a given animal. 



