Abstract
An apparatus named “electronic rheotome” was devised by us for electric stimulation of the eye with sinusoidal alternating currents. The electronic rheotome enables us to start the alternating currents at 0°phase and to stop them at 180°or 360°phase. Combining the electronic rheotome with an A.C. oscillator, we can settle precisely such factors of a stimulus as intensity, duration, frequency and phase of the beginning and the termination, that the measurements of the electric threshold can be made accurately. The electronic rheotome of the 2nd type, furthermore, can produce currents of different forms such as square, anodal and cathodal waves.
As a first application of the electronic rheotome we examined the dependence of the electric threshold of the eye upon duration and frequency of the sinusoidal alternating currents. It was found that the characteristics of the strength-duration curve at any frequency are quite different between both ranges above and below a definite frequency in the vicinity of 50 to 60 cps. The threshold values for a frequency above 60 cps. differ strikingly according to whether the phase at the termination of the current is 180°or 360°, while the threshold values for a frequency below 50 cps. decrease steadily with the increase in duration of stimulation, till they reach the lowest value in the duration of 2 to 3 cycles, and they thereafter remain almost constant, no matter at which phase of 180°or 360°the stimulating currents end. That is, a few cycles at the onset of the stimulating currents cause the summation of stimuli. This summation of stimuli takes place most remarkably in the neighbourhood of 20 cps.
