230 COMPARATIVE ELECTRO-PHYSIOLOGY 



observed a second phase to set in, in which the upper surface 

 became relatively negative to the lower. This negative 

 change, which he called the ' after-effect,' he described as 

 taking place at that moment at which the mechanical effect 

 of excitation also made itself evident. 



This negative phase called by him the ' after-effect '- 

 Burdon Sanderson regarded as connected with those electrical 

 changes which had been observed by Kunkel to be induced 

 by movement of water in the tissues. The first effect on the 



FIGS. 150, 151, 152. Records!of Electrical Responses of Different Leaves 

 of Dion<ea according to Fundamental Experiment of Burdon Sanderson 



Fig. 150. Positive response of certain leaves of Dioncca. Time-marks 



20 per second (Burdon Sanderson). 

 Fig. 151. Diphasic response of leaf of Dioncca ' in its prime.' Positive 



followed by negative. Time-marks 10 per second (Burdon Sanderson). 

 Fig. 152. Positive response of same leaf when 'modified' by previous 



stimulation. Time- marks 10 per second (Burdon Sanderson). 

 The above records were obtained with capillary electrometer. 



contrary, which immediately preceded this, and was charac- 

 terised by relative positivity of the upper surface, he regarded, 

 as already mentioned, as the true excitatory or action-effect. 

 The following is from his summary : 



* The first phase of the variation --the effect which 

 immediately follows excitation, ancl has an opposite 

 sign to the after-effect, and a much higher electro-motive 

 force does not admit of a similar explanation : for it 

 cannot be imagined that a change which spreads over 

 the whole lamina in less than one-twentieth of a second 

 can be dependent on migration of water. The excita- 

 tory disturbance which immediately follows excitation 



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