ix ELECTRICAL EXCITATION OF NERVE 177 



while the height of the closure twitch is unaltered, or even 

 increases perceptibly. The same occurs with descending currents, 

 only in this case the electrodes must be brought nearer the 

 muscle in order to abolish the opening twitch, since here the 

 kathode first, and -only later the anode, falls within the normal 

 region. The height of the closure twitch then increases con- 

 spicuously, showing once more that excitability to closure stimuli 

 is more vigorous at normal points of the nerve than at those 

 which are altered by the action of the potash although opening 

 twitches are not discharged in the normal nerve, and never fail to 

 appear in the other. 



If, at a not too advanced stage of KN"0 3 action, the nerve 

 while giving approximately equal make and break twitches at all 

 points when excited with weak constant currents is moistened 

 sufficiently with 0*6 / Q NaCl, it soon appears that while the 

 make twitches are at first unaltered, the height of the break 

 twitches decreases more and more the longer the bath is con- 

 tinued. Finally, after 1015 minutes, they disappear altogether, 

 with uniform or even much stronger currents, leaving the closure 

 twitch, as at the beginning of the experiment, the sole effect of 

 excitation in either direction (Fig. 194, g, h). 



It was stated above that the break twitches discharged by 

 weak currents in consequence of potash treatment are identical 

 in character with those observed under the action of alcohol to 

 precede the delayed break twitch II, which at first makes a 

 solitary appearance. Twitches analogous to these latter are 

 altogether wanting in " potash nerves." 



It is a priori not improbable that treatment of a more 

 restricted area with KNO 3 might locally induce the conditions 

 favourable to the appearance of " primary opening twitches " 

 (break twitch I), thus enabling weak ascending or descending 

 currents, with given position of electrodes, to produce an effective 

 opening excitation. 



If the same method be employed as in the above-described 

 local treatment of nerve with concentrated saline, currents of low 

 intensity being used for excitation, a different reaction follows 

 in the nerve according as (after applying a pad of cotton-wool 

 soaked in 1 % KN0 3 to one or the other electrode) the solution 

 of potash acts upon the electrode proximal to the muscle or to 

 the centre. In both cases the size of the make twitch during 



VOL. II N 



