Abstract
Previous work with pedigree cultures of ParamæcEcium 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 ParamæcEcium 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 paramæcia on a “varied environment” dependent upon the intrinsic stimuli from the frequent changes in the medium, or is a “constant” medium of hay infusion unfavorable 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 Paramecium 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 conducive to the unlimited development of this culture without conjugation or artificial stimulation.
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