Experimental physiology.

  • Sharpey-Schäfer, E. A. (Edward Albert), Sir, 1850-1935.
Date:
1912
Catalogue details

Licence: In copyright

Credit: Experimental physiology. Source: Wellcome Collection.

Provider: This material has been provided by Royal College of Physicians, London. The original may be consulted at Royal College of Physicians, London.

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    FATIGUE OF MUSCLE AND NERVE 43 metronome), to close and open a gap between two mercury cups m the circuit. Use maximal stimuU. Keep the point of the lever —which must be free-weighted—against the smoked paper, and record every contraction. In this way a continuous fatigue curve IS obtained, exhibiting the effect of fatigue, not only in the extent of contraction but also on the extensibility of the muscle both in rest and in contraction. Notice the staircase (gradual rise of the ordinates) at the beginning of the curve and the contracture (permanent contraction remainder) near its termination. Garry the experiment to complete exhaustion—until the stimuli produce no further perceptible effect. Then allow the preparation to rest, keeping it moist with Kinger's solution. After 15 or 20 minutes again test the effect of a stimulus. Notice that there is a certain amount of recovery from the fatigue, even in a preparation such as this in which no blood is circulating. In muscle in which the circula- tion is maintained fatigue comes on more slowly and is more rapidly recovered from, since the circulating blood removes the fatigue products. Reaction of the fatigued muscle.—Cut across a muscle which is completely- fatigued, and apply blue litmus paper to it. Notice that the paper is reddened (production of acid fatigue products). Compare the reaction with that of a piece of fresh, unfatigued muscle. Muscle which has died and passed into rigor—whether natural or the effect of heat (see p. 41)—is also acid. Onset of the fatigue in a muscle-nerve preparation: Bernstein's experiment.—Arrange an experiment in the manner shown in the diagram (fig. 40). Dissect out both nerve-muscle preparations of a frog and place both nerves near the spinal cord on a single pair of elec- trodes connected through a short-circuit key with the secondary coil. Another pair of electrodes—which should be non-polarisable (p. 7)— is connected with one of the nerves in such a manner that the current furnished by three Daniell cells (shown below in the diagram) can be led into the nerve in an ascending direction. When the mercury key of this circuit is closed the constant current from the Daniell cells blocks the nerve, and the nerve impulses generated by the induction shocks fail to pass to the muscle. Stimulate both nerves by induction shocks. The muscle the nerve of which is free to conduct is speedily fatigued : the other one shows no signs of contraction; on removing the block by opening the mercury key it at once responds to the stimuli, and its contractions show no evidence of fatigue even after long faradisation of its nerve. Fatigue in voluntary contraction.—This is investigated by the