Beef extract as " constant" culture medium 121 
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Beef extract as a "constant" culture medium 
for Paramecium aurelia, 
By LORANDE LOSS WOODRUFF and 
George Alfred baitsell. 
[From the Sheffield Biological Laboratory of Yale University.] 
Previous work with pedigree cultures of Paramcecium aurelia 
and caudatum has apparently shown that the life history of these 
forms, when bred continuously on infusions of hay made up exactly 
the same from day to day, tends to run in a cycle which terminates 
with the death of the culture. Previous work (Woodruff) has 
also shown that Paramcecium aurelia may be bred indefinitely 
on a culture medium which is frequently varied. 
In view of these results the following question is of interest: 
Is the longevity of paramaecia on a "varied environment" de- 
pendent upon the intrinsic stimuli from the frequent changes in 
the medium, or is a " constant" medium of hay infusion unfavor- 
able because it lacks some elements which are essential for the 
continued existence of this protozoon? To test this point beef 
extract was chosen because it was believed that it contains all 
of the essential elements. After a series of preliminary tests, a 
.025 per cent, solution of Liebig's extract of beef was decided upon 
for the experiments. 
Briefly, it may be stated that the solution of beef extract 
employed has proved (during the seven and one half months of 
the experiment) to be practically as favorable a medium for the 
reproduction of the pedigree culture of Paramcecium aurelia as 
the "varied" culture medium; and therefore the conclusion seems 
justified that this culture can, in all probability, be continued 
indefinitely on this medium, and that it is the "composition" of 
the medium rather than "changes" in the medium which is con- 
ducive to the unlimited development of this culture without con- 
jugation or artificial stimulation. It is also believed that a 
"constant" medium of beef extract, in this or similar solutions, 
will prove to be a favorable culture medium in which to breed 
pedigree cultures of paramaecia for certain physiological studies, 
