. Eight lectures on the signs of life from their electrical aspect . FlG. 40.—Nerve-muscle preparation ; to demonstrate the muscular contractions associated with the positive anodic after-current in nerve. by means of a double key, a strong battery-current which is to traverse the nerve in an ascending direction as figured (the galvanometer meanwhile being plugged). During the passage of the constant current, the muscle remains quiescent, but when I break the current, the muscle, as you see, contracts, and will contract for a longer or shorter period. Immediately after breaking the battery cur
. Eight lectures on the signs of life from their electrical aspect . FlG. 40.—Nerve-muscle preparation ; to demonstrate the muscular contractions associated with the positive anodic after-current in nerve. by means of a double key, a strong battery-current which is to traverse the nerve in an ascending direction as figured (the galvanometer meanwhile being plugged). During the passage of the constant current, the muscle remains quiescent, but when I break the current, the muscle, as you see, contracts, and will contract for a longer or shorter period. Immediately after breaking the battery current, I unplug the galvanometer, when you witness a strong and permanent positive deflection, signifi- cant of an action-current in the nerve of the same direction as that of the previous battery-current. The deflection is not absolutely permanent, it is gradually falling, the muscle will not remain indefinitely contracted, it will relax sooner or later ; the positive current in the nerve, and the contraction of the muscle, are associated effects of a state of local irritation or action in the previously anodic region of the nerve. You know that the current from an active to an inactive spot of nerve runs in the nerve from active to inactive (in the galvanometer from inactive to active, the latter pole being therefore called nega- tive), and that the active spot acts like the zinc of a voltaic couple—is in brief a zincative spot. Therefore you know from the direction of this after-current that the active spot from which the irritation to the muscle proceeds is post-anodic as to its source in the nerve itself. § 59. Locality of reaction.—Polar inequalities of effect have
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