The Relationship of the Nutritive State of the Prey Organism Paramecium aurelia to the Growth and Encystment of Didinium nasutum

SYNOPSIS. Only well fed Paramecium aurelia, grown either monoflorally or on a mixture of 2 species of bacteria, are adequate to maintain optimal fission rates and encystment rates for Didinium nasutum. Progressive starvation of paramecia prior to their being fed to didinia leads to decreased fission rates, the appearance of abnormal cells and a loss of ability to encyst by the didinia. This depression can be fully overcome by allowing the didinia to feed again upon well nourished paramecia. A minimum of 45 well‐fed paramecia is required daily for each Didinium if maximal fission rates are to be maintained. Encystment and fission appear to be mutually exclusive processes, but encystment rates are related to fission rates and seem to be exclusive of the density of the didinial culture.