Effect of hormones and related compounds on the multiplication of Tetrahymena

The vertebrate hormone triiodothyronine, the commonly occurring animal and plant hormone serotonin, and the plant alkaloid gramine, chemically related to the latter, stimulated the multiplication of Tetrahymena. Neither epinephrine nor gibberellin had such an effect. These experimental observations support the previous suggestion that unicellular animals possess structures capable of responding to certain hormones, which do not seem to elicit specific responses of the unicellular animal, but rather act through the activation of certain general functions.