278 



Prof. J. C. Bose. On Electromotive Wave [May 21, 



a potentiometer the galvanometer spot may be brought back to the 

 original position.) The shifting of the zero will not affect the general 

 result. The direction of this more or less permanent current, clue to 

 the small P.D., gives no indication of the direction of current of 

 response ; the direction of the latter is determined by the rule that the 

 responsive current flows towards the more excitable point. The effect of 

 the mechanical stimulus is to produce a transient electromotive force 

 which is algebraically superposed on the existing P.D. The deflection 

 will take place from the modified zero, to which the spot returns during 

 recovery. I give four records (fig. 2) : in (a) A is touched with Na2C0 3 

 (which is an excitant) : a permanent current flows from B to A : response 

 to stimulus is in the same direction as the permanent current (positive 

 variation) ; in (b) A is touched with a trace of oxalic acid (which 

 depresses the excitabilily), the permanent current is in the same direc- 

 tion as before, but the current of response is in the opposite direction 

 (negative variation) ; in (c) A is touched with dilute KHO (3 parts in 

 1000), the response is exhibited by a positive variation; in (d) A is 

 touched with stronger KHO (3 parts in 100), the response is now 

 exhibited by a negative variation. The last two apparently anomalous 

 results are due to the fact (which will be demonstrated later) that KHO 

 in minute quantities is an excitant, while in larger quantities it is a 

 depressant. 



(a) Kesponse when A is treatel with, sodium carbonate — an apparent positive 



variation 



(J) „ „ „ „ „ oxalic acid — an apparent negative varia- 



tion 



(c) „ „ „ „ „ very dilute potash — positive variation. 



(d) „ „ rt „ „ strong potash — negative variation. 



This response is up when A is more excitable and down when B is more 

 excitable. 



Lines thus indicate direction of permanent current. 



