146 COMPARATIVE ELECTRO -PHYSIOLOGY 



been given in fig. 80. Using this arrangement, the specimen 

 is clamped at one end, the vibration-head being at the other. 

 Electrical connections are now made with the two dia- 

 metrically opposite points, A and B, of which one, say A, is 

 the upper, and B the lower. In a tissue which is isotropic, 

 vibrational stimulus will induce equal and simultaneous 

 excitation at the two points A and B. The effect of any 

 given agency is tested by applying it locally, say at A, and 

 observing the resultant variation of the response. I shall 



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KlG. 101. Photographic Record showing Negative, Di-phasic, and 

 Positive Resultant Responses in Tin under appropriate modifications 

 of excitation of the two contacts 



here give examples of results obtained by both these methods, 

 thus affording an indication of the extent of their applicability 

 in various investigations. 



We have seen in the previous chapter that the application 

 of strong solution of potash will abolish the excitability of 

 a tissue. Using the Longitudinal Balance, I took a petiole 

 of Bryophyllum and first made such adjustments that the 

 right ' up ' and left ' down ' responses were almost equal. 

 On now producing simultaneous excitation of the two ends, 

 a di-phasic response was obtained, due to the fact that the 

 left-hand point was the quicker to respond. Strong solution 



