Abstract
Some media are described which inhibit bacterial growth, but are favorable to protozoan development. A purification technique, which takes advantage of geotropic responses, was devised and used successfully with 7 species of protozoa, including flagellates and ciliates. The method was also used with a Spirillum. For one flagellate which could not be purified in this manner, a procedure involving chemical sterilization was employed. Paramecium caudatum was purified, but failed to develop subsequently in the absence of living microorganisms. Four of the protozoa which were purified ingest other microorganisms normally. The work shows that purified protozoa grow well under proper conditions, and then they can be studied culturally and biologically, like bacteria.