140 THE PHYSIOLOGY OF NERVE 



tissue is inconsiderable. Contrariwise, however, it is evident that 

 its storative quahties are excellent, because while the interruption of 

 its blood supply eventually leads to a reduction of its irritability and 

 conductivity, this depression is not quickly forthcoming; in fact, the 

 nerves of the cold-blooded animals may retain these properties for 

 a surprisingly long period of time after their excision. 



Fatigue of Nerve. — Nerve-tissue possesses certain qualities which 

 fortify it against excessive dissimilation and thus prevent it from 

 entering the state of fatigue with the same readiness as other tissues. 

 The earlier experiments pertaining to the development of fatigue in 

 nerve, were made with nerve-muscle preparations. In all these in- 

 stances the contraction of the gastrocnemius muscle served as the index 

 of activity. It is a well-known fact that the repeated stimulation of 

 any musculomotor nerve eventually leads to a cessation of the contrac- 

 tions, but this result has been proved to be due to a fatigue of the end- 

 plates and not to an exhaustion of the nerve itself. Consequently, 

 experiments of this kind cannot yield reliable results unless the muscle 

 is protected in some way against these impulses, while the nerve is not. 

 A block of this kind may be established quite easily with the aid of 

 curare. To begin with, it must be shown that each stimulation of the 

 nerve produces a contraction of the muscle. If a solution of curare is 

 now applied to the latter, the ensuing paralysis of the motor plates 

 prevents the impulses from reaching the effector^ until the action of 

 this drug has again weakened. During the interim, therefore, the 

 nerve may be stimulated without producing a muscular reaction. By 

 this means it has been found that nerves may be made to conduct 

 impulses for many hours without becoming fatigued. Similar tests 

 have been made with the vagus nerve, the inhibition of the heart being 

 prevented during these repeated stimulations by the administration 

 of atropin.2 ^g goon as the action of this drug weakened after many 

 hours, the stimulations again became effective. Very similar results 

 have been obtained by stimulating the chorda tympani of the sub- 

 maxillary gland after the administration of atropin. Secretion was 

 resumed in this instance as soon as the action of this drug diminished 

 sufficiently to permit the impulses to break through.^ It has also been 

 shown that a galvanometer connected with a nerve indicates a wave 

 of negativity with every excitation, and even if these stimulations are 

 continued for many hours. Thus, Beck'* has stimulated the cervical 

 sympathetic nerve during seventeen hours without succeeding in 

 greatly lessening the dilatation of the pupil. 



1 Bernstein, Pfliiger's Archiv, xv, 1877, 289; Wedenski, Zentralblatt der med. 

 Wissensch., 1884, and Bowditch, Jour, of Physiol., vi, 1885, 133. The effect of 

 curare may be removed within a few minutes by the salicylate of physostigmin. 

 (Diirig, Zentralbl. fiir Physiol., xv, 1902, 75.) 



2 Scana, Arch, fur Anat. u. Physiol., 1891, 315. 



2 Lambert, Compt. rend., 1894, 511; also see: Mascheck, Sitzungsber. d. 

 Wiener Akad., xcv, 1887. 



4 Pfluger's Archiv, cxxii, 1908, 585. 



