SYNOPSIS. Several strains of particle‐bearing and particle‐free Paramecium aurelia have been cultivated in an axenic medium composed of proteose peptone, trypticase, yeast nucleic acid, MgSO4.7H2O, TEM‐4T (diacetyl tartaric acid esters of tallow monoglycerides), stigmasterol and a mixture of vitamins. The “yeast fraction,” an indispensable component of previous media used for the cultivation of these ciliates has been replaced by a mixture of trypticase, yeast nucleic acid and TEM‐4T. Particle‐bearing animals of stock 299 lambda, 138 mu, and 139 pi maintain their particles when cultivated in the medium, whereas particle‐bearing animals of stock 51 kappa, 225 kappa and 114 signia do not. With the exception of stock 92 (syngen 3) the medium appears to be selective in its ability to support the growth of animals of the even‐ but not odd‐numbered syngens of P. aurelia. Maintenance of the particles was dependent only to a small degree upon environmental conditions brought about by changes in pH and temperature. Division of the particles was found to be comparable with the division of the protozoan. Methods for the growth, maintenance and mass cultivation of particle‐bearing P. aurelia are given in detail.

SYNOPSIS. A method was developed for the isolation and purification of crystalline, highly refractile bodies found in the cytoplasm of a symbiote‐free strain of the marine hymenostome ciliate, Parauronema acutum, strain 110–3. Chemical analysis of the purified refractile bodies revealed an abundance of the purines, hypoxanthine and guanine. It was evident from studies involving the use of 14C‐labeled precursors that both hypoxanthine and guanine are derived from higher purine derivatives. We postulate that these bodies are excretory in function and that guanine and hypoxanthine are major endproducts of purine metabolism of P. acutum.

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SYNOPSIS DNA extracted from macronuclei of axenically cultured Paramecium aurelia has been characterized with regard to its kinetic complexity. Renaturation of macronuclear DNA from this protozoon appeared to follow 2nd order kinetics and revealed the presence of 2 components: a main component comprising ∼96% of the genome which renatured slowly and a minor component comprising ∼4% of the genome which renatured at a rate ∼3000 faster than the main component. The value of the kinetic complexity of the main component has been estimated at 3.8 × 1010 daltons and that of the minor component at 1.45 × 107 daltons. It is suggested that the macronucleus contains ∼840 diploid copies of the slowly renaturing component; for each copy of the latter there are ∼100 copies of the fast renaturing component.

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