Parameciidae 



117 



table I — Effect of Liver Extract, Kidney and Yeast on the Growth of 



Paramecium. 



Medium 



Water+kidney*** 



(4 it 



tt tt 



Water+kidney+dead yeast 



tt t* tt tt 



tt tt tt tt 



Water+kidney+ living yeast 



11 tt tt tt 



tt it tt tt 



Lilly's extract+kidney-f dead yeast. 



Lilly's extract+dead yeast 



H tt tt tt 



tt tt it tt 



Liver extract+kidney-f dead yeast. 



tt tt 



Transplant 



Negative 



Positive 



Negative 



Positive 



*** Water=sterile tap water; kidney = fresh rabbit kidney; Lilly's extract = extract prepared from Eli- 

 Lilly and Company's liver extract No. 343; liver = rabbit liver extract prepared in this laboratory; — = 

 dead; ±.=doubtful growth; +=weak growth: ++=fair growth; +-r-+=good growth; -f-- r -- r -+=lux 

 uriant growth. 



(From Glaser and Coria, 1933) 



several months in the new medium, and the Protozoa were then returned 

 to "basic medium" and the whole procedure repeated. Potato or carrot 

 water is prepared by autoclaving 2 gram pieces of the vegetable in tubes 

 with 10 cc. of water. For use, 2 cc. of the liquid so obtained is diluted 

 with 10 cc. of sterile water. Yeast extract is prepared in the following 

 way. Pure cultures of yeast are grown on dextrose agar in Blake bottles 

 for 5 to 7 days at room temperature. The growth is washed and centri- 

 fuged three times with 50 cc. of sterile water and 2 cc. of the sedimented 

 cells are then ground for 5 hours in a sterile mechanical grinder consisting 

 of two ground glass tubes one of which, the pestle, fits snugly within the 

 other and is turned by an air turbine motor (see Glaser and Coria 1934a 

 for details). Thirty cc. of sterile water are then added and the mixture 

 stirred for another 20 minutes. This ground yeast suspension is centri- 

 fuged 1 5 minutes to remove the larger particles and is then sterilized com- 

 pletely (i.e. freed of intact yeast cells) by filtration through a sterile 

 Berkefeld V filter. Small amounts of such a yeast extract when added 

 to any of the media greatly stimulated the growth of the Protozoa. 

 Extracts filtered through Berkefeld N filters or prepared from yeast killed 

 chemically or by heat did not stimulate. It should be noted that even 

 the best yeast extracts could not be substituted for the intact heat killed 

 yeast cells in the special medium devised for the Paramecia. 



