x ELECTROMOTIVE ACTION IN NERVE 293 



definite state of excitability (not always present in the same 

 degree) in the cooled nerve, while on the other a pro- 

 nounced closure tetanus with ascending direction of current is 

 usually under these conditions of experiment exceptional ; and 

 further, the subsequent and much stronger positive effect soon 

 defeats the initial heterodrornous action. It is thus intelligible 

 that the latter should disappear, or be present as a trace 

 only, on shifting the galvanometer electrodes away from the 

 transverse end of the nerve, and thereby rendering the essential 

 conditions of its appearance still more unfavourable. Lastly, 

 it can hardly be necessary to state that the application of 

 strong ascending constant currents may obstruct the negative 

 fore-swing, as well as the transmission of the closure excita- 

 tion ; it is, moreover, absent in isoelectric leads from the un- 

 injured nerve, as, under all conditions, in preparations of warmed 

 frogs. 



We have already noted that Engelmann found a marked 

 negative variation in the demarcation current of medullated 

 frog's nerve on opening the battery current, provided the excita- 

 tion took place under conditions in which a tetanic opening 

 excitation might be expected. 



As such, for instance, must be reckoned adequate strength 

 and duration of the ascending exciting current, but most of all 

 the disposition of the nerve to persistent excitation so frequently 

 alluded to. Under favourable circumstances the negative opening 

 effect on leading off from the transverse end of the nerve is not 

 inferior in magnitude to the negative closure effect with descending 

 excitation. 



No definite conclusion as to the nature of the positive 

 anelectrotonic closure effects can be deduced from the above 

 experiments, since these exhibit along the whole extrapolar anodic 

 portion of the nerve, a reaction essentially similar to that of non- 

 medullated molluscan nerve, unless it be reckoned as a distinction 

 that they appear in the former with weaker currents, and at a 

 much greater distance from the part of the nerve traversed by 

 the current. Since, as has been shown, the anelectrotonic altera- 

 tions in non-medullated nerve can scarcely be explained otherwise 

 than by a physiological change of state transmitted from the anode, 

 it seems highly probable that a similar process occurs likewise 

 when medullated nerve is traversed by current on the side of the 



