ADAPTATION OF CUTANEOUS TACTILE RECEPTORS : VI. INHIBITORY EFFECTS OF POTASSIUM AND CALCIUM.

1. Both solutions of Ringer plus fifteen times the normal K content, and solutions of Ringer plus fifteen times the normal Ca content markedly hasten the adaptation of single freely branching axon endings in frog's skin to repetitive air puff stimuli. 2. The K effect is produced more rapidly than is that of Ca. The K effect is reversible by washing with Ringer's solution, while the Ca effect is not. The Ca inhibition can, however, be reversed and recovery effected by washing with K rich solutions. 3. Evidence is discussed which indicates that Ca probably plays no rôle in normal adaptation, and the experiments are interpreted as substantiating the hypothesis of adaptation due to K.