LONGITUDINAL IMPEDANCE OF THE SQUID GIANT AXON

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Abstract
Longitudinal alternating current impedance measurements have been made over the frequency range from 30 cycles per sec. to 200 kilocycles per sec. on the giant axon of the squid., Loligo pealii. Large sea water electrodes were used and the inter-electrode length was immersed in oil. The impedance at high frequencies was approx. as predicted theoretically on the basis of the poorly conducting dielectric characteristics of the membrane previously detd. For the large majority of the axons, the impedance reached a maximum at a low frequency and the reactance then vanished at a frequency between 150 and 300 cycles per sec. Below this frequency the reactance was inductive, reaching a maximum and then approaching zero as the frequency was decreased. The inductive reactance is a property of the axon and requires that it contain an inductive structure. The variation of the impedance with interpolar distance indicates that the inductance is in the membrane. The impedance characteristics of the membrane as calculated from the measured longitudinal impedance of the axon may be expressed by an equivalent circuit containing inductance, capacity, and resistance. For a square cm. of membrane the capacity of 1 [mu]f with dielectric loss is shunted by the series combination of a resistance of 400 ohms and an inductance of 1/5 henry.

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