. Electro-physiology. Electrophysiology. 22 ELECTRO-PHYSIOLOGY CHAP. is required, in which the positivity of the lower surface diminishes slowly, before the second phase again appears distinctly. The stronger the positivity of the lower surface ab initio, the less can it be increased by excitation of the leaf, and conversely, the plainer will be the primary opposite variation. In an unmodified leaf with outgoing leaf-current (Burdon- Sanderson's "descending" current), the variation consequent on excitation is again found, on leading off from opposite points of the respective surfaces
. Electro-physiology. Electrophysiology. 22 ELECTRO-PHYSIOLOGY CHAP. is required, in which the positivity of the lower surface diminishes slowly, before the second phase again appears distinctly. The stronger the positivity of the lower surface ab initio, the less can it be increased by excitation of the leaf, and conversely, the plainer will be the primary opposite variation. In an unmodified leaf with outgoing leaf-current (Burdon- Sanderson's "descending" current), the variation consequent on excitation is again found, on leading off from opposite points of the respective surfaces, to be diphasic. The first "entering" phase (ascending in the leading-off circuit), which lasts about a second, and in which the upper and previously positive leaf-surface. PIG. 145.—Photogram of the variations of an outgoing leaf-current, on exciting one lobe and leading oft'from the other (cf. Fig. 143). 10 divisions of the time-marking correspond to 1 sec. (Burdon-Sanderson.) suddenly becomes negative, is often preceded by a momentary alteration in the opposite direction, as shown in Fig. 145. Here again the opposite (outgoing or descending) " after-effect" (second phase) only appears plainly in the first excitation, and owing to its very slow decline is wanting in those that immediately succeed it. The most important conclusion from these observations is that the leaf of Dioncca is excitable in both the unmodified and the modified condition, independent of the direction of the rest current, save that the galvanic effects of excitation are reversed pari passu with the reversal of the current of rest. It is evident that the " modifications" of the leaf-current consequent on repeated excitation are only the after-effect of the slowly declining second phase of the excitatory variation. For exact measurements of time, as well as of the of the varia- tion, Burdon-Sanderson employed a pendulum myograph arranged as a rheotome, which in swingi
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