. Electro-physiology. Electrophysiology. 180 ELECTRO-PHYSIOLOGY CHAP. changes of form (Fig. 76). Fresh muscles, or those which, though older, are still in a state of considerable tonic contraction, generally appear quite insensible to induced currents. The advantages of a sustained passage of current over brief " current impacts " is also seen in tetanising excitation periodicaU// repeated. Fick pointed out that the rapid make and break, by, hand, of an intrinsically effective constant current, generally failed to excite smooth molluscaii muscle—yet the duration of the single impacts
. Electro-physiology. Electrophysiology. 180 ELECTRO-PHYSIOLOGY CHAP. changes of form (Fig. 76). Fresh muscles, or those which, though older, are still in a state of considerable tonic contraction, generally appear quite insensible to induced currents. The advantages of a sustained passage of current over brief " current impacts " is also seen in tetanising excitation periodicaU// repeated. Fick pointed out that the rapid make and break, by, hand, of an intrinsically effective constant current, generally failed to excite smooth molluscaii muscle—yet the duration of the single impacts here is considerable; if it is still further lessened, stronger and stronger currents will be required to pro- duce any excitation. This is especially striking in excitation with a rapid succession of induced alternating currents, and Fick states " that in the same circuit that closes the secondary coil of an ordinary induction apparatus, a frog's muscle may fall into the most lively tetanus, while the molluscan muscle shows no sign of excitation," and that this even occurs with currents. FIG. 76.— Contraction curves of adductor muscle of Anodonta, excited by single make and break induction currents (s and o) of increasing strength («, at greatest distance of coil). that are strong enough to throw the muscles of the experimenter's hand into tetanus (4). Engelmann's observations on the ureter (5) naturally fall into line with these experiments on the smooth adductor muscle of molluscs. Here, too, it is easy to demonstrate that the make contraction occurs only when the duration of current exceeds a certain limit, which is lower in proportion with the strength of the current. This is plain from the accompanying table (Engelmann). Strength of current in rheochord resistance. 4000 cm. 500 „ 50 „ 25 „ 15 „ 12 „ 11 „ 10-5 „ Minimum closure, required to produce contraction. quarter second. 1 2 3 4 5 6. Please note that these images are extracted from scann
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