290 ELECTRO-PHYSIOLOGY CHAP. 



more pronounced, but homodromous, electromotive alterations 

 appear under all circumstances, and independent of the excita- 

 bility of the preparation, or of the pre- existence of a rest 

 current in the vicinity of the exciting tract, under the influence 

 of the current. These increase rapidly with further shortening of 

 the intermediate tract. The striking independence of the first- 

 named, weaker effects in regard to current intensity (they may 

 even decline in magnitude as the intensity of the current increases), 

 and length of intermediate tract, makes it hardly doubtful that 

 this is not ordinary electrotonus, but an effect of excitation. 



The reaction of non-medullated molluscan nerve, in which true 

 katelectrotonus seems to le altogether absent, is therefore comparable 

 under similar conditions only with that tract of medullated 

 nerve which is most remote from the part excited. 



The electromotive alterations in medullated nerve below an 

 ascending current exhibit several marked differences from the 

 corresponding effects on the kathodic side, irrespective of the 

 opposite direction of the deflections on the galvanometer. 



On leading off from the peripheral end of a sensitive cooled 

 nerve with an artificial section (it is usual to take two juxtaposed 

 sciatics), and passing a weak ascending current through the 

 central cut-end (1 Dan. EW '= 1020 cm.), there is invariably 

 a positive variation of the (compensated) current of rest on 

 closing the exciting circuit (cf. Table I.) ; this variation averages 

 515 degrees of the scale, and in most cases exceeds the corre- 

 sponding effect of the descending current under similar conditions 

 (Biedermann). It is altogether independent of the presence or 

 absence of a demarcation current (an important point), and is 

 present at almost equal strength in the perfectly uninjured and 

 isoelectric nerve also (Tables II. and III.). 



