Electro-physiology electrophysiolog02bied Year: 1896-98 ELECTRO-PHYSIOLOGY CHAP. surface of the ventricle. The galvanometer, of course, shows the same thing with the rheotome method. In order rightly to interpret this ' diphasic action current,' it is essential to determine the rate at which the excitation (? the effect of stimulus) spreads in the parenchyma of the leaf. Burden-Sanderson used a pendulum rheotome for this purpose, with which it is easy to determine the time between the moment of excitation and commencement of the consequent electrical variation of the leaf-current. This curre
Electro-physiology electrophysiolog02bied Year: 1896-98 ELECTRO-PHYSIOLOGY CHAP. surface of the ventricle. The galvanometer, of course, shows the same thing with the rheotome method. In order rightly to interpret this ' diphasic action current,' it is essential to determine the rate at which the excitation (? the effect of stimulus) spreads in the parenchyma of the leaf. Burden-Sanderson used a pendulum rheotome for this purpose, with which it is easy to determine the time between the moment of excitation and commencement of the consequent electrical variation of the leaf-current. This current was, as before, led off from the middle of the opposite surfaces of a lamina. In a preliminary series of experiments, the exciting electrodes were placed on either side of a leading-off electrode on the upper FIG. 148. surface of a leaf, so that a straight line connecting the two passed through the leading-off contact. The first perceptible trace of phase I. of the excitatory variation generally appeared 0'041 sec. after the moment of excitation. If time is required for the spread of the excitatory activity, it is evident that the ' latent period ' must be very much longer (with unaltered position of the leading- off electrodes) when the stimulus is applied to the lobe that is not led off. That this is so appears from Burdou-Sanderson's experiments, where the interval between excitation and beginning of the variation as a rule exceeds 0'073 sec. Accordingly, if we estimate the distance between the two points excited in succession at 6 rnm., the transmission of excitation must occur at about 200 mm. per sec. (at a temperature of 30°—32° C. in air saturated with aqueous vapour). An even greater disparity between the latent periods in the two cases might have been expected, supposing that, as in muscle, there were no perceptible latent period in the
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