

RESPONSE OF NERVE 727 



numerous experiments (figs. 350 and 353). The fact that 

 under feeble E.M.F. the variation of excitability is opposite 

 to that under moderate E.M.F. can be demonstrated with 

 great simplicity by means of the subjective response of 

 sensation. A wound was made on the back of the hand, and 

 the application of a dilute solution of salt caused a moderate 

 irritation. The application of kathode to this wound now 

 rendered the irritation intolerably painful, while that of the 

 anode at once made it soothing, removing even the normal 

 discomfort due to the salt, These effects coming under 

 Pfliiger's generalisation that kathode enhances excitability, 

 while anode depresses held good so long as the acting 

 E.M.F. was about 1*5 volt. But when the acting E.M.F. 

 was reduced to '5 volt, the kathode was found to induce 

 a soothing sensation, whereas the anode became painful. 



I have also found that the passage of a current pro- 

 foundly modifies the conduction of excitation in a directive 

 manner, according as the excitation has to travel with or 

 against it. In the simplest cases, where the polarising elec- 

 trodes are so far apart as to eliminate the direct excitatory 

 effect of the poles, and using a feeble current, I have shown 

 that excitation travels better electrically uphill, that is to say, 

 against the current, than down, or with it. Thus the normal 

 responses to transmitted stimulation are found to be enhanced 

 when the polarising current is against the direction of trans- 

 mission. A polarising current in the same direction as that 

 of excitation, has, on the other hand, the effect of retarding 

 it. The normal responses are then diminished, or even 

 reversed to positive, by the diminution or abolition of the 

 power of true conduction (figs. 345, 346, 347). 



The various effects described as polarisation-increment 

 and decrement have been shown further to be due to the 

 increased galvanometric negativity of the more excited of 

 two points, the responsive current being algebraically sum- 

 mated with the existing electrotonic current. The greater 

 excitation of one of these two points was also shown to be 

 due to the greater intensity of excitation conducted to it, or 



