Abstract
Experiments were undertaken to determine (1) the relationship between the volume of culture fluid and the division rate of Infusoria, and (2) the effect of cell proximity on the division rate. The Infusoria studied were pedigree races of Paramecium aurelia, Paramecium caudatum, and Pleurotricha lanceolata. The experiments comprised four lines of each species bred in 2, 5, 20 and 40 drops of hay infusion. Forty drops were approximately equal to 1 cc. At the end of five day periods the average per diem division rate was obtained for the four lines in each volume.
In the set of experiments with different volumes of culture medium, the average per diem rate was higher in the larger volumes, as shown by the following data, based on the averages for twenty-seven experiments lasting through a period of five days each for the three species mentioned, or nine experiments per species: animals in 2 drops, 0.92 division; in 5 drops, 1.03 divisions; and in 20 drops, 1.20 divisions. Eighteen of the experiments, or six experiments per species, included four lines each in 40 drops with an average per diem division rate of 1.27. Woodruff 1 in his studies on the effect of excretion products of Protozoa on their rate of reproduction obtained equivalent results and interpreted the lower division rate in smaller volumes of medium as due to the effect of the excretion products of the animals.
The second set of experiments differed from the above in that it was confined to a pedigree race of an hypotrichous infusorian and, instead of one animal, two animals were bred together on each slide, in order to determine whether, as Robertson 2 maintained in his studies on Enchelys farcimen Ehr., cells mutually accelerate their division rate by the production of a chemical agent or “autocatalyst”.
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