VIII. 



THE investigation of negative variation of the nerve current, 

 with the improved methods for which we are indebted to du Bois- 

 Reymond, leads to results which modify in many respects the doc- 

 trines taught by its discoverer respecting it. 



I may premise that in future communications I shall frequently 

 have the opportunity of recurring to the negative variation, and 

 shall confine myself here to a short discussion of the fact that the 

 negative variation of the nerve current caused by electrical tetani- 

 sation is generally followed by a positive variation, which commences 

 at the close of the stimulation and thus immediately follows the 

 negative variation. 



Du Bois- Raymond's statement, 'that after tetanic stimulation 

 the needle of the multiplier only returns more or less incompletely 

 to its state of rest,' a phenomenon which he attributes to loss of 

 electromotive power of the nerve in consequence of the preceding 

 stimulation, accordingly appears to be insufficient. My observa- 

 tions were made in December and January, partly with cold, 

 partly with warm frogs (E-. esculenta) ; the former term I apply 

 to frogs brought straight from the cellar, the latter to those kept 

 for some days in a room the temperature of which never fell below 

 i50. 



The tract of nerve lying between the stimulating electrodes I 

 call the stimulated region. It always consists of a portion of the 

 sciatic plexus a little below the ligatured upper end, and was 5 mm. 

 in length. The portion lying between the leading off electrodes 

 will be designated the galvanometer tract. It is always at the 

 peripheral end of the nerve. The portion between the lower 

 stimulating electrode and the upper galvanometer electrode will 

 be called the intermediate tract. 



