98 ELECTRO-PHYSIOLOGY CHAP. 



crico-arytaenoideus posticus muscle earlier than the constrictor of 

 the glottis, and Semon and Horsley (53) determined a peripheral, 

 differentiating action of ether upon the laryngeal muscles in the 

 same sense. 



The differences of excitability in functionally differing nerve- 

 muscle organs are, however, most striking iu certain invertebrates, 

 and most of all in the claw of the crayfish. Eichet and Luch- 

 singer (54) first observed that weak excitation of the claw-nerve 

 opened, and stronger excitation closed, the claw. Tick (55), who 

 had made objections (subsequently shown to be unfounded) 

 to Eollett's first experiments on the frog's leg, tried to explain 

 the observations of Eichet and Luchsinger on purely mechanical 

 grounds, as due to the anatomical relations of the excited muscles. 

 This, however, was easily disproved (Biedermann, 56). If the 

 claw-nerve is excited with the alternating current of an induction 

 coil, by inserting two platinum points through the second or 

 third joint (after arranging for the simultaneous graphic record of 

 the changes of form in both antagonist muscles, by means of 

 separate levers for each muscle) the same fact appears as in the 

 normal uninjured claw, i.e. as a rule the abductor muscle con- 

 tracts with weaker, the adductor with stronger excitation of the 

 nerve. 



When the current is strengthened by gradually pushing up the 

 coil, the response to excitation being read off each time, it is found 

 in a muscle free of tomis that the abductors alone react at a given 

 distance of coil. With further strengthening of stimulus, the 

 effects increase up to a certain limit, and then decrease and finally 

 disappear, without any simultaneous change of form in the 

 adductor muscle. The coils may then be brought much closer 

 together without producing any perceptible excitatory effects in 

 either muscle. The adductor muscle first comes into play at a 

 given strength of stimulus, and responds to each subsequent 

 excitation up to the maximum of current intensity, while the 

 abductors give no perceptible reaction. The abductor, however, 

 frequently contracts at the close of excitation, with the coil 

 pushed home (Figs. 165, 166). 



In every such case there is a certain interval of current 

 intensity, during which neither of the antagonist muscles reacts 

 to excitation from the nerve. The magnitude of this " neutral 

 zone" varies in different cases. Moreover, it should be noted that 



