[200] _Thörner_: “Weitere Untersuchungen über die Ermüdung des markhaltigen Nerven: Die Ermüdung in Luft,” etc. Zeitschr. f. allgem. Physiologie Bd. X, 1910. [201] _Vészi_: “Zur Frage des Alles oder Nichtsgetzes beim Strychninfrosche.” Zeitschr. f. allgem. Physiologie Bd. XII, 1911. On the basis of these facts it is readily understood when a level of equilibrium of lower intensity has been reached that excitation produced by weak faradic stimulation must have weaker effects than when strong stimuli are applied, for when the system assumes a heterobolic type as the result of relative fatigue weak stimuli bring about weak, and strong, stronger excitation. Consequently, during interference induced by a second series of excitations, in the first case we have the conditions favorable for inhibition, in the second for those of summation. If we also assume that this characteristic alteration of the isobolic character of the elementary nerve fibers which has been shown to occur in fatigue, as seen when continued faradic stimulation is employed, develops immediately after the beginning of stimulation then we can readily understand the various kinds of effects produced by interference observed in the reflex response following weak and strong faradic stimulation to the different nerves in spite of the fact that the nerve in the state of rest is a system isobolic in type. Experimental evidence, therefore, must be brought forward to show that faradic stimulation of short duration produces the above-mentioned alteration in the character of the system. _Thörner_ in his experiments on the nerve stimulated it faradically at least four minutes and always found after this that excitation was reduced. After shorter intervals of stimulation _Thörner_ made no test of the state of excitation. It is, however, highly probable that a reduction of excitation is much more quickly reached. Indeed, we are unavoidably compelled to accept the assumption that even after the first single stimulus of the faradic current, alterations of a slight degree are present which, after repeated stimulation, become constantly greater and give to the system a heterobolic character. As a result of fatigue, as we have already seen, the refractory period becomes more and more prolonged. As the individual shocks in faradic stimulation follow each other at regular intervals, a necessary consequence is that the shocks are operative before the refractory period has completely disappeared, otherwise _Thörner_ could not have obtained fatigue produced by continued stimulation. The intervals of the individual shocks must be somewhat shorter than the duration of the refractory period, even in fatigue of a very slight degree. It is very interesting in this connection that _Thörner_ invariably obtained positive evidences of fatigue by the application of stimuli at the rate of 10–12 per second. When the number of stimuli per second was less than this the above-mentioned