in ELECTRICAL EXCITATION OF MUSCLE 285 



already produced an obvious, persistent K.C.C. ; on the contrary, 

 the stage of augmented response in most cases eludes observa- 

 tion (on account of its excessively short duration) if the 

 intensity of the polarising current is insufficient to discharge a 

 maximal closure twitch in the muscle. It is therefore a universal 

 principle to employ only the weakest battery currents when the- 

 object is to demonstrate a marked increase of response in the 

 kathodic points of the fibres at a given stage of polarisation, 

 since it might otherwise be easily overlooked. Hermann (42), 

 together with Pfliiger and Nasse (in older experiments), finds that 

 " in nerve, as well as in muscle, the effect of a given induction 

 current is increased by homodromous constant currents, and de- 

 pressed (to abolition) by opposite currents." Beginning with the 

 weakest constant currents, the increase of excitation from homo- 

 dromous variations of current gives way to diminution when the 

 strength of the constant current exceeds a certain limit ; Hermann 

 obtained the same results in a still more unexceptional manner 

 by using battery currents for excitation. 



In Tables I. and II. (supra) the twitches discharged by the 

 test stimulus immediately after closure of the battery current 

 were approximately maximal. There is thus an a priori proba- 

 bility which receives experimental confirmation, that the responsi- 

 tivity of the kathodic points of fibres in a muscle traversed ~by 

 current increases up to a certain limit with the intensity of the 

 polarising current. This limit, however, is very low ; in our own 

 experiments it was reached as a rule at 12 cm. deriving 

 circuit, with 2 Dan. as the battery. Beyond this limit, excita- 

 bility diminishes, as has been shown, in proportion with the 

 strength of the polarising current. 



It is just in the case in which the intensity of the latter is so 

 low that each increase of it produces a corresponding augmentation 

 of the excitatory effect of a homodromous induction current, that 

 the increase in height of twitch corresponding to increased duration 

 of closure of the battery current, recorded by v. Bezold, might be 

 expected ; but in no instance has it made its appearance. 



What conclusions then may be drawn from these experiments ? 

 Since we know that the induction current used as test stimulus 

 generally produces visible excitation at the kathode only, i.e. at 

 points of fibres which, during the closure of the polarising 

 current, are already in a state of persistent excitation, the con- 



