548 COMPARATIVE ELECTRO-PHYSIOLOGY 



minutes. The consequent responses are seen to be uniform, 

 and to take place by that diminution of resistance which we 

 already know to constitute the normal mode of response 

 (fig. 331). In order to obtain some idea of the magnitude 

 of these resistance variations the balance was upset at the 

 end of the response record, to the extent of 4,000 ohms. 

 The deflection seen to the right of the figure represents the 

 effect of this variation of resistance. The normal resistance 

 of the tissue, including that of the non-polarisable electrodes 

 was, as stated before, 400,000 ohms. The resistance of the 

 electrodes themselves was 50,000 ohms. That of the tissue 



FIG. 331. Response Records by Resistivity Variation, in the Nerve 

 of Fern ; Stimuli at Intervals of Five Minutes 



Response to stimulation is by the negative variation or diminution of 

 resistance. The record to the right shows deflection due ; to variation 

 of resistance of 4,000 ohms. 



alone was thus 350,000 ohms. The variation of resistance 

 induced by stimulus, therefore, was, in the present case, 

 approximately i per cent. 



In order, next to determine whether the resistance 

 variation was a consequence of the responsive change of 

 form, or an independent expression of the fundamental 

 molecular change, I clamped a nerve of fern suitably, at 

 its two ends, to prevent any possible change of length, the 

 two non-polarisable electrodes being led off in such a way 

 as to include a certain length of the specimen. On 

 carrying out the experiment in this manner I obtained 

 response by diminution of resistance, exactly as in the last 



