92 ELECTRO-PHYSIOLOGY CHAP. 



excitability is, of course, the reaction of the terminal organ as 

 discharged by a stimulus of definite magnitude, and nearly all 

 experiments bearing on this point relate to electrical excitation of 

 motor nerves the electrical stimulus being the sole test that is 

 sufficiently accurate. The relations to be determined at any 

 point of the nerve between magnitude of stimulus and magnitude 

 of effect coincide in the main with those shown above to obtain 

 in direct excitation of the muscle. If a tract of nerve is stimulated 

 by gradually increasing single induction currents, it will be found 

 that currents of which the intensity lies below a given limit 

 (" liminal " value) do not excite, while with increasing current 

 intensity the height of twitch is also augmented the rise, according 

 to Tick (40), being proportional within a certain range, while, accord- 

 ing to Hermann (40), it is at first rapid and then more gradual. 

 The connecting line between the summits of the single twitches 

 would thus, according to Tick, rise obliquely to its maximum, 

 according to Hermann it would form a curve concave to the 

 abscissa. 



Seeing that there is a discharge of potential energy in excita- 

 tion of nerve, as in direct excitation of muscle, and indeed in any 

 excitation of living matter, it is a priori evident that there can 

 be no constant relation between strength of stimulus and 

 effect. The excitability of a nerve can only be compared with 

 other organs, or nerves, or different points of the same nerve, 

 by employing the "liminal value" of the electrical stimulus as 

 the (reciprocal) measure of excitability. Eosenthal (41) was 

 thus able to establish the fact that the specific excitability of 

 nerve-substance is greater than that of striated muscle, or, as it may 

 be expressed, that the indirect is greater than the direct excitability 

 of muscle. Eosenthal applied the sciatic nerve longitudinally to 

 a curarised gastrocnemius. Induction currents were then led 

 through both nerve and muscle, which, as the resistances of the two 

 were approximately equal, were proportionately distributed between 

 both sections, i.e. current flowed in both tissues at equal density. 

 The indirectly excited muscle first began to twitch as the 

 current was gradually strengthened by pushing up the coil, i.e. 

 nerve responds to weaker electrical excitation. The results 

 obtained by this method at different points of the same nerve are 

 also of interest. 



Budge (42) observed that "the sciatic nerves are more 



