Abstract
The contractions of sciatic-gastrocnemius preparations of Rana pipiens were recorded isotonically by means of a free-weighted lever loaded with 20 or 30 gm. The preparations were repeatedly stimulated with maximal break shocks at intervals of one second. At one-half minute intervals a tetanising current (10 per second) was applied for 5 seconds. The following changes in amplitude of contraction after tetanus, as compared with the amplitude before tetanus, appeared:
1. Normal Muscle. A. Indirect Stimulation. In a fatiguing muscle an increase in amplitude occurred and the percent increase became greater (up to 800%) as fatigue progressed. No change was observed in unfatigued muscle, and tetanus during this time diminished the increase to be expected in fatigue. The enhancement of contractions in a fatigued muscle was greater after tetanus (for 5 seconds) than after a rest period of similar duration, and the enhancement persisted for a greater number of stimulations.
B. Direct Stimulation. Fine copper wires, inserted into the belly of the gastrocnemius, were employed. No increases appeared in most of the experiments. It is concluded that in those fatigued preparations in which enhancement occurred after each tetanus some muscle fibers were being stimulated indirectly. This has been proved by the studies on curarised preparations.
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