Myasthenia gravis / by Charles S. Myers.

  • Charles Samuel Myers
Date:
1902?]
Catalogue details

Licence: In copyright

Credit: Myasthenia gravis / by Charles S. Myers. Source: Wellcome Collection.

    17/46 page 319
    the muscle were prevented by the introduction of a constant current passing along its nerve between the muscle and the point of stimu¬ lation by the tetanising current. Now it was found that, if the tetanising current were applied directly to the apparently exhausted muscle, it would again enter into tetanus; while, if in the second preparation the constant current were finally broken, the previously resting muscle would at once contract briskly, thus showing that neither the nerve fibres nor the muscle had been in reality exhausted by the tetanising current. By a process of exclusion. Waller inferred that end plates are the first to undergo fatigue. There are other experiments, which likewise point to the delicate constitution and ready vulnerability of end plates. They seem to be by far the weakest point in the muscle-nerve preparation. Having exposed the sciatic nerve of a recently killed rabbit. Waller (ss) found that the application of induction shocks to the nerve within half an hour after the death of the animal caused no contraction of the muscles innervated, although the muscles still responded to direct electrical stimulation. Thereupon he cut out the nerve, proved its current of rest by the aid of a galvanometer, and obtained well-marked negative variation by applying to the nerve a tetanising current; that this variation resulted from a purely physiological activity, he assured himself by observing that tetanic excitation of the nerve no longer produced an effect on the variation current, if a tight ligature had been previously passed round the nerve between the point of electric stimulation and the non-polarisable electrodes leading to the galvano¬ meter. Again, Abelous (^9) severed the sciatic nerve of a frog, and found that when the spinal cord was stimulated long enough to cause muscular exhaustion, the paralysed muscles also became fatigued, but earlier to indirect (nervous) than to direct (muscular) stimulation. Finally, the experiment, by Waller (^s), of tetanising a muscle alternately by direct and indirect stimulation, when the contractions induced by the latter show far the more evident fatigue, seems to make good the general conclusion that in fatigue of a .muscle-nerve preparation the end plate is the first structure to be affected. It has been supposed that nerve fibres owe their relative in¬ exhaustibility to their protective sheath of Schwann. Mott (4*^) observed that the products of degeneration in peripheral nerves are removed with strikingly greater rapidity than the same products occurring in the central nervous system. In muscle fibres we know that fatigue rapidly ensues if acid phosphates, phosphoric acid, kreatin or lactic acid are allowed to accumulate. Even mental exertion has been shown by Mosso to cause muscular fatigue; and it is well known that the introduction of the blood of a fatigued animal into the circulation of a normal animal will produce in the latter all the cardiac, respiratory, and other signs of exhaustion. Thus, so far as our physiological knowledge carries us, fatigue in
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