Colpidium campylum cultures can be enriched by feeding with Bacterium coli, which is tolerated in fairly concentrated culture by this ciliate but not by most others. Cultures of C. campylum sterile for bacteria and other organisms were achieved in yeast autolysate (dilutions 1:2 to 1:50) and 1% peptone-glucose (after Butterfield). Sterile cultures, but little growth, of Glaucoma scintillans were accomplished with yeast extract. Loxocephalus granulosus has been grown in sterile ciilture in yeast extract and peptone-glucose solutions. Colpidium colpoda was grown in double or triple systems of bacteria, but could not be grown in sterile culture. The order of appearance of these organisms in the usual hay infusion (Glaucoma, Colpidium campylum, Colpidium colpoda, Stentor) is interpreted in terms of the bacterial activity and decomposition products present at different times in the culture medium.