ELECTRIC CONTROL OF EXCITATION
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polar variation of excitability. By means of a Pohl's commutator 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 conducting power in Mimosa. A, storage 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 "off" without variation of resistance; E, E′, electrodes of induction coil for stimulation; C, choking coil; G, micro-ammeter.
