Elimination of Kappa Particles from `Killer' Strains of Paramecium aurelia by Treatment with Chloromycetin

CERTAIN strains of Paramecium, known as `killers', contain in their cytoplasm particles, called `kappa particles'¹, which are Feulgen-positive, and stain with Giemsa after acid hydrolysis². Killers liberate into the culture medium a substance lethal to Paramecium not containing kappa particles, known as `sensitives'. Kappa particles have many of the properties of cytoplasmic genes³, but their size (0.2-0.5 µ in length), and their staining reactions, suggest that they may be parasitic micro-organisms^3-5 such as the rickettsiæ, viruses of the psittacosislymphogranuloma group, or even small bacteria.