EXCITABILITY DETERMINED BY INTERFERENCE 14$ 



is seen the di-phasic effect which was induced when the 

 excitation of the right was made to lag slightly behind that 

 of the left, by the adjustment of the striking-rod at a 

 small minus angle. The first of the two twitches, which is 

 downwards, indicates the relatively earlier excitation of the 

 left-hand contact. As the phase-difference was increased 

 progressively as in (d) and (i), it is seen that the constituent 

 elements of the di-phasic response are increased corre- 

 spondingly. It is also clear from this that, having obtained 

 the null-effect, if any agents were afterwards applied locally 

 which would make the excitation of the one point earlier 

 than that of the other, we must then expect the null-effect 

 to be modified to di-phasic. An earlier ' up ' twitch would 

 now indicate that the right-hand contact, having had its re- 

 action quickened, was the first to respond ; an earlier ' down ' 

 twitch the opposite. 



We thus see how the conversion of the null-effect into a 

 resultant * down ' negative or ' up ' positive, could .be utilised 

 as a test of the excitatory or depressing nature of a given 

 reagent. We also see how the conversion of this null into a 

 di-phasic effect would give us indications as to the change 

 of time-relations induced by the reagent. I shall here, 

 before going on to describe the results obtained with plants, 

 give a photographic record (fig. 101) of certain positive, nega- 

 tive, and di-phasic effects obtained in the electrical response 

 of the inorganic substance, tin, under appropriate modification 

 of the excitability of its two contacts by various chemical 

 reagents. 1 



Turning now to the question of the determination of 

 the effects of the various reagents by the Method of 

 Interference, we may, as we have seen, cause simultaneous 

 excitation of right and left, by means of the apparatus which 

 has just been described, and which I shall distinguish as the 

 Longitudinal Balance. There is, again, another and simple 

 method of accomplishing the same object, by means, namely, 

 of the Diametric Balance -, the diagram of which has already 



1 Bose, Response in the Living and Non-Living, p. 115. 



L 



