iv GENERAL PHYSIOLOGY OF NERVOUS SYSTEM 227 



stimulus is weakened, or made less frequent, the reaction reappears. 

 Under normal conditions these effects of fatigue are manifested 

 only in muscle and particularly in the motor end-plates ; but we 

 shall see that under special circumstances the nerve trunk too may 

 exhibit similar paradoxical phenomena, so that the experiments 

 of Sclriff and Wedensky cannot be taken as a positive proof of 

 the non-fatigability of nerve. 



The experiment of Bowditch (1885) is simpler and less 

 ambiguous. After curarising a cat, using artificial respiration, 

 he divided the sciatic and tetanised for a long time with an in- 

 duction current, which produced no effect upon the muscles of the 

 leg, owing to the paralysis of the motor end-plates. After two to 

 three hours of artificial respiration the paralysis induced by the 

 curare wears off, the animal gradually recovers, and the effects of the 

 excitation of the sciatic appear in the form of an irregular tetanus. 

 Lambert substituted atropine for curare, and was able to show the 

 non-fatigability of the secretory fibres contained in the chorda 

 tympani. After many hours of ineffectual stimulation of the 

 nerve the sub-maxillary gland began to secrete as the poison 

 disappeared gradually. 



A more direct proof of the relative inexhaustibility of nerve 

 was given by Wedensky with the galvanometer and telephone. 

 He showed that the electrical phenomena (negative variation) 

 characteristic of functional activity undergo no perceptible altera- 

 tion after protracted stimulation ; and that two nerves excised 

 from the body, one being at rest, the other exposed to prolonged 

 stimulation, perished simultaneously. 



These researches as a whole show that nerve fibres, unlike 

 other parts of the central and peripheral nervous system, exhibit 

 no signs of exhaustion, even after protracted activity : the fact that 

 a nerve is still capable of reacting to direct stimulation after the 

 response of the muscle had ceased proves as Waller pointed out 

 that the organs which connect the nerve with the muscle, i.e. 

 the motor end-plates, are much more easily fatigued than the 

 muscle and nerve. It is probable that the waste products developed 

 by the muscle during tetanus have some significance in the 

 production of exhaustion in the end-plates, as they may exert 

 a toxic action on the motor nerve -endings similar to that of 

 curare (Abelous). 



This relative inexhaustibility is not, however, characteristic of 

 all nerves. Garten (1903) discovered a non-medullated nerve 

 (olfactory of pike) which readily becomes fatigued. On stimulat- 

 ing it with a series of induction currents at brief intervals, the 

 action current observed by the capillary electrometer diminished 

 after a few stimulations, but it increased again after a pause. 

 Even niedullated frog's nerve under abnormal conditions manifests 

 phenomena which cannot be interpreted otherwise than as fatigue 



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