Cytological and Cytogenetical Studies on <i>Paramecium polycaryum.</i> V. Lethal Interactions in Certain Stocks*

Abstract

SYNOPSIS. Evidence is presented for killer and sensitive animals in Paramecium polycaryum. The killer animals excreted in the culture medium a lethal substance which killed the sensitive animals. The lethal substance was unstable at high temperatures and was completely precipitated by centrifugation at 10,000 rpm for 30 minutes. Comparative immunity to killing by killer animals was shown to be possessed by some animals of certain sensitive stocks. Attempts to find a cytoplasmic particle comparable to “kappa” in P. aurelia in killer animals were not successful.