IX ELECTRICAL EXCITATION OF NERVE 183 



especially appropriate. In favourable cases a weak descending 

 current discharges break twitch II shortly before the explosion 

 into tetanus. A similar experiment was made by Griinhagen 

 (36). But if this proves that break twitch II and Patter's 

 tetanus (as well as the closure tetanus) are in many cases due, not, 

 as Pfliiger thought, to disappearance of anelectrotonus (or entrance 

 of katelectrotonus), but to latent stimuli, which, in themselves 

 inadequate to excite the muscle, first become effective when the 

 excitability of the nerve is raised after the disappearance of 

 anelectrotonus (or during an existing katelectrotonus) it must be 

 admitted that in many cases an adequate opening excitation of 

 the same character appears without any previous state of latent 

 excitation (cooled nerves). Nor is this surprising in view of the 

 relations between rise of excitability and excitation, as described 

 above. On the other hand, the nature of break twitch I is still 

 unexplained, although the conditions of its appearance are known 

 more precisely than before. 



Arguing from experiments in which break twitch I appears 

 immediately after making a (mechanical, chemical, or thermal) 

 cross-section in the close proximity of the anode, it follows that 

 the demarcation current developed by this injury must be in 

 causal connection with the appearance of break twitch I. Yet 

 this cannot be in the sense that the raised excitability in the 

 vicinity of the cross-section (the cause of which will be discussed 

 below) renders weak opening stimuli effective ; for this hypothesis 

 seems to be sufficiently contradicted by the foregoing data. Griin- 

 hagen's view that the appearance of the make twitch, when a 

 fresh section is applied to the nerve near the anode, is to be 

 regarded primarily as a " product of summation " (" on the one 

 hand, of the intrinsically inadequate excitation, consequent on the 

 opening of the descending current," i.e. the anodic stimulus ; " on 

 the other, of the continuous, weak, mechanical stimulus of the 

 incision/'), must be regarded as disproven. For apart from the 

 fact that an after-effect of simple division, lasting for hours 

 (and the disposition to the discharge of break twitch I does 

 last that time in the vicinity of the cross -section), is highly 

 improbable it may further be urged against Griinhagen that the 

 effects of the make excitation would then have to be propor- 

 tionately strengthened, with uniform position of electrodes, and 

 ascending direction of current, which is not the case. We have 



