. A text-book of physiology : for medical students and physicians . the great easewith which it may be varied as to rate and as to intensity. Onaccount of the very brief duration of the induced current it is dif-ficult to distinguish between the effects of its opening and Stimulation of the Nerve by the Galvanic Current.—When however, we employ the galvaniccurrent, taken directly from a bat-tery, as a stimulus, we can, ofcourse, allow the current to passthrough the nerve as long as weplease and can thus study the effectof the closing of the current asdistinguished from that of the
. A text-book of physiology : for medical students and physicians . the great easewith which it may be varied as to rate and as to intensity. Onaccount of the very brief duration of the induced current it is dif-ficult to distinguish between the effects of its opening and Stimulation of the Nerve by the Galvanic Current.—When however, we employ the galvaniccurrent, taken directly from a bat-tery, as a stimulus, we can, ofcourse, allow the current to passthrough the nerve as long as weplease and can thus study the effectof the closing of the current asdistinguished from that of the open-ing, or the effect of duration ordirection of the current, etc. Du Bois-Reymonds Law of Stim-ulation.—When a galvanic currentis led into a motor nerve it isfound, as a rule, that with allmoderate strengths of currents thereis a stimulus to the nerve at themoment it is closed, the making orclosing stimulus, and another whenthe current is broken, the breakingor opening stimulus, while duringthe passage of the current through the nerve no stimulation takes. Fig. 30.—Schema of the arrange-ment of apparatus for stimulating thenerve by a galvanic current: _ b, Thebattery; k, the key for opening andclosing the circuit; c, the commutatorfor reversing the direction of the cur-rent; + the anode or positive pole;— the cathode or negative pole. THE PHENOMENON OF CONDUCTION. 87 place: the muscle remains relaxed. We may express this factby saying that the motor nerve fibers are stimulated by the mak-ing and the breaking of the current or by any sudden changein its intensity, but remain unstimulated during the passage of cur-rents whose intensity does not vary. The Anodal and Cathodal Stimuli.—It has been shown quite con-clusively that the nerve impulse started by the making of the currentarises at the cathode, while that at the breaking of the currentbegins at the anode, or, in other words, the making shock orstimulus is cathodal, while the breaking stimulus is anodal. Thisfac
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