Fig. 36.
Curve of action current of two nerves, one of which is stimulated (plain line) whilst the other remains at rest (dotted line). After decrease of irritability of the stimulated nerve in nitrogen, oxygen is introduced into the chamber and irritability increases again. Then the previously resting nerve is stimulated in nitrogen and the stimulated nerve remains at rest. (After Thörner.)
Scheme showing course of fatigue (plain line) and recovery (dotted line) of the nerve as it is manifested on testing the irritability with tetanic stimuli, when fatigue and recovery alternate at equal intervals. The curve shows at the beginning an apparent increase of irritability corresponding to the “Treppe” of the muscle. (After Thörner.)
Fig. 37.
Scheme showing course of fatigue (plain line) and recovery (dotted line) on testing the irritability of the nerve by single induction shocks. In fatigue irritability sinks at first rapidly, then more and more slowly until a state of equilibrium is reached. Recovery shows the same in reverse succession. (After Thörner.)
As a result of all these investigations, linked together in a systematic series, the proof has now been obtained that the nerve like all other living substances is fatigable. Its fatigue is solely the manifestation of a prolonged refractory period and the extension of the latter by continuous stimulation is, as in all aërobic substances, a result of relative deficiency of oxygen.
Fig. 38.