The Fine Structure of Kappa in Killer Stock 51 of Paramecium aurelia. Preliminary Observations

The killer trait in Paramecium aurdia depends upon the presence of a cytoplasmic genetic particle, kappa (1). Animals possessing kappa liberate into the culture medium in which they live a poison, paramecin, to which they themselves are resistant; animals lacking kappa are killed by this substance. Stained preparations and phase microscope observations of fixed and unfixed kappa reveal, in stock 51, two types of particles: smaller bodies ("non-brights") with no detectable internal structure and larger forms ("brights") associated with paramecin activity and containing a highly refractile body (2). In polar view, this inclusion is circular with a central dark core. In side view, the refractile body usually is square (0.5/~) but occasionally is divided into two equal halves by a dark band (-core) that unites with the kappa matrix at either end of the refractile body. Preer's varied methods of staining the refractile body were unsuccessful (2); but the rest of the kappa particle in whole mount preparations of killer animals was reported to be uniformly Feulgen-positive.