vni CONDUCTIVITY AXD EXCITABILITY OF NERVE 97 



(M. tibialis antic., perouseus, flexor tarsi anterior and posterior, M. 

 exteusores, abductores digit, and iuterossei) ; with stronger excita- 

 tion of the common nerve, on the other hand, the extensors of the 

 foot move backwards and downwards along with the adductors 

 of the toes. The first group (" flexors ") are mainly, if not 

 exclusively, supplied by the peroneal nerve, the second by the 

 tibial nerve, so that in this preparation (frog's leg) all, or at any 

 rate nearly all, the fibres which subserve the antagonistic groups 

 of muscles are found in the two primary branches of the 

 common nerve. In subsequent experiments Kollett recorded 

 the isolated contractions of the antagonistic groups of muscles, 

 showing that only the flexors really contract at first, and not the 

 extensors ; increase of stimulus iuduces weak extension along 

 with more pronounced flexion, and finally the extensor exceeds 

 the flexor contraction. By making the antagonist muscles 

 work against each other on the same lever (antagonistograph), 

 and record the effects of this opposite action, Eollett finally con- 

 vinced himself that when the nerve is excited, the flexors respond 

 to weak stimuli with a greater yield of work than the extensors. 

 The flexor movements increase with augmentation of stimulus up 

 to a certain point, at which they are overtaken by the extensors ; 

 there is an intermediate stage of " struggle " between the anta- 

 gonistic reactions. The same differences in excitability of flexors 

 and extensors obtain in the rabbit ((/. Frl. Volklin, Hermann's 

 Handb. i. 1, p. 113). Mechanical and chemical stimuli produce 

 the same effect as electrical excitation (Osswald, 50). Osswald, 

 by careful graduation of the shocks from an apparatus modelled 

 upon Heideuhain's tetano-motor, succeeded (with minimal excita- 

 tion of the nerve) in evoking flexor movements from frogs 

 as well as toads, which changed to extensor movements on 

 gradually increasing the stimulus. The extensors ultimately got 

 the upper hand, and tetanus in extension made its appearance. 

 The same effect was produced by chemical stimulation with sodium 

 chloride and other salts. 



Similar differences in the excitability of the nerve -muscle 

 organ appear with other antagonistically working muscles. 

 Griitzner (51) found that during weak excitation of the vagus 

 the constrictors of the glottis, during stronger excitation the 

 dilatators, contracted. Frankel and Gad (52) showed that the 

 effect of gradually cooling the recurrent nerve was to cut out the 



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