Studies on the life cycle of Paramecium

A year ago I reported to this society the results obtained up to that time on the life cycle of Paramecium when subjected to a varied environment. I wish now to bring the results up to date (May 26, 1909). A culture of Paramecium aurelia (caudatum) was started on May 1, 1907, with a “wild” individual isolated from a laboratory aquarium, and during the twenty-five months which have elapsed since that time it has been under daily observation. Infusions of hay and grass together with any material that may be found in the normal habitat of Paramecium have been employed as a culture medium. The possibility of contamination by cysts or “wild” Paramecia has been eliminated by boiling the infusion. Daily isolation of an individual from each of the various lines of the culture has enabled an accurate record of the division rate to be kept and has precluded the possibility of endogamous conjugation.