polar variation of excitability. By means of a Pohl's com-

mutator or reverser, the constant current can be maintained either "with" or "against" the direction of transmission of excitation. The transmission in the former case is

Fig. 45. — Complete apparatus for investigation of the variation of conduct ing power in Aiimosa. A, storai^e cell; S, potentiometer slide, which, by alternate movement to right or left, continuously increases or decreases the applied E. M. F. ; K, switch key for putting current "on" and " oflf " without variation of resistance ; E, E', electrodes of induction coil for stimulation ; C, choking coil ; &, micro-ammeter.