Further Studies on the Sterile Culture of Paramecium

Abstract

Hydrolyzed nucleic acid (both RNA and DRNA) was substituted for the heat-labile fraction of pressed yeast juice in the culture of P. multimicro-nucleata. Growth equal to that obtained with pressed yeast juice was obtained in a 1% proteose-peptone medium to which was added hydrolyzed nucleic acid and the heat-stable fraction of pressed yeast juice. Cultures were carried through 29 transfers in this medium. A mixture of guanylic and cytidylic acids was as effective as the hydrolyzed nucleic acid. P. aurelia was also successfully grown in this medium. All attempts to substitute a mixture of vitamins and other known substances for the heat-stable fraction were unsuccessful. Also attempts to substitute mixtures of amino acids, C sources and salts for the proteose-peptone medium failed.