49O COMPARATIVE ELECTRO-PHYSIOLOGY 



excitation transmitted. In the first four records of the present 

 series the induced enhancement of conductivity is shown by 

 the occurrence of up-responses only. The fifth record, how- 

 ever, shows a marked preliminary twitch in the negative 

 direction, followed by an up-response of some amplitude. 

 This shows that the excitatory effect reached the right end 

 E later than the left, though the intensity still remained 

 greater. The continued action of the reagent subsequently 

 reduced the intensity also, so that this diphasic ultimately 

 became converted into a purely monophasic down-response, 

 gradually increasing to a maximum. In fig. 298 we observe 

 the depression of conductivity by a stronger dose of 2 per 

 cent, solution of Na 2 CO 3 , applied on the right-hand side at C. 

 Here, again, we can see the separated effects of the two 

 elements of conductivity that is to say, the intensity of the 

 effect transmitted and the speed of transmission. In the first 

 few responses of this series we see the diminished intensity 

 of transmission to the right giving rise to resultant responses 

 which are entirely downwards. Later, this transmission of 

 enfeebled excitation becomes delayed also, and by the phase- 

 difference thus induced we obtain the growing diphasic effects 

 which have already been fully explained on p. 144, fig. 100. 

 Owing now to this growing difference of phase, the two 

 opposed effects no longer neutralise each other to the same 

 extent as before, and we obtain increasing amplitude of both 

 the constituent phases. The down-curve in the diphasic 

 response represents the earlier arrival, and relatively greater 

 intensity, of effect at the left contact E'. And the up-curve 

 shows the later arrival of the less intense effect at the right- 

 hand contact E. It is thus clearly seen that conductivity 

 includes two different elements of speed and intensity which 

 may not in all cases be coincident. 



I shall next describe experiments which will demonstrate 

 the variation of conductivity versus that of responsive excit- 

 ability under the action of the same reagent. In animal nerve 

 responsive excitability is diminished by the action of strong 

 solutions of neutral salts, and potassium salts induce greater 



