Abstract
Nernst's law of stimulation (stimulus = current √ time) has been proven for currents from 0.0002 to 0.001 seconds duration, but Lapique showed that a minimum time was necessary and was different for different tissues. A minimal current flowing infinitely which just causes a contraction is called the rheobase, the rheobase is then doubled and the time for stimulation is measured, this time is called the chronaxie. Owing to the uncertainties of the form of many of the currents used in determining chronaxie or to the undesirability of the form of the current (asymptotic) we have adopted a different procedure.
Our studies of the electric stimulation of muscle with alternating current have led us to believe that what is called the “summation of stimulus” is due to the direct current component of the alternating current. The induction coil gives a current having a unidirectional competent, as shown by Washburn, who inserted a silver coulometer in series with the secondary of an induction coil and obtained a deposit of silver.
We have used a Vreeland oscillator, giving a current of pure sine wave form with no direct current component, the frequency of which can be changed by small gradations between 7000 and 300 cycles per second. Since the time of stimulation is one-half of a cycle, the minimum time of stimulation may be determined, our results on the stimulation of gastrocnemius muscle of the frog in Ringer's fluid being 0.000079 seconds. With curarized muscle it was found that the minimum the for stimulation was increased to 0.00009 seconds. The tongue muscle required 0.0001 3 seconds. The minimal time for stimulation of smooth muscle could not be determined by means of the oscillator because a low enough frequency could not be obtained, but this presents no difficulty since Englemann was able to determine it in 1870.
This is a preliminary report.
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