Abstract
The relation of chronaxie to the frequency of alternating electric currents capable of stimulating muscle is shown in the following table. The alternating current was derived from a General Radio Company oscillator, No. 377, and silver pin electrodes 5 mm. apart coated with AgCl by electrolyzing 1% NaCl with 6 volts for 10 seconds. These were stuck into the muscle and the chronaxie was determined by the condenser method.
The above table indicates that the threshold of duration of current from oscillator is about 0.05 of the chronaxie in case of fish and frog. With the crab and scallop the results are uncertain owing to the uncertainty of the determination of such long chronaxies by the condenser method. Since the energy required to stimulate is at a minimum at the chronaxie, it seems best to use muscles with short chronaxies for measuring the conductivity of the muscle with the stimulating current (using telephone for detection), so that the muscle will become stimulated in a small fraction of a cycle.
Lapique has shown that chronaxie varies rapidly after excision of tissue, and similar results are obtained for the highest frequency capable of stimulating the muscle. The gastrocnemius of the green frog was excised at 4:50 P. M. and immediately placed in moist chamber and stimulated at 70 kilocycles; at 4:55, 60 kilocycles was the highest frequency that would stimulate it; at 5:20, 30 K. C., 5:30, 28 K. C., and 5:45, 20 K. C.
No great difference in chronaxie was observed between bony fish and elasmobranch (dogfish) and the absence of bones in the latter made it convenient. No difference was observed between the green frog and bull frog. The muscle was pressed between silver electrodes. It was found that a film of AgCl did not lower the impedance. The measurements were made with a Wheatstone bridge with equal ratio arms.
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