CHARACTER OF TRANSMITTED IMPULSE 163 



through 10 mm. is therefore "63 second. The next record 

 was taken when the intervening length of 10 mm. in the 

 petiole was moderately lowered in temperature by the 

 application of cold water. This cooling should be com- 

 menced immediately after the previous responsive fall of the 

 leaf. This not only gives sufficient time for the localised 

 cooling of the petiole but also avoids the excitatory disturb- 

 ance of the pulvinus caused by sudden application of cold to 

 the petiole. During the localised cooling of the petiole the 

 leaf erects itself and becomes fully sensitive when the time 

 arrives for the application of the next stimulus. Record 2 

 exhibits the effect of moderate cooling ; the transmission 

 period is now prolonged, the difference between the two 

 records being a time-interval of '8 second. On the assump- 

 tion that the effect of cooling had remained localised, it is 

 seen that the lowering of temperature had prolonged the 

 period of transmission through the 10 mm. of the petiole 

 from -63 second to 1-43 second. The conductivity has 

 thus been reduced by more than half. 



In record 3 is seen the effect of further lowering of 

 temperature by placing small fragments of ice on the strip 

 of cloth. The excitatory impulse initiated by the maximal 

 stimulus of induction-shock had hitherto been unfailingly 

 transmitted. But under the action of intense cold the impulse 

 is arrested. In order to show that the abolition is not due 

 to the depression of motile excitability of the pulvinus, 

 record 4 is taken of the effect of direct stimulation. An 

 inspection of the record shows that the motile excitability 

 has undergone no change. It is thus clear that the impulse 

 initiated by the stimulus has been arrested by the physio- 

 logical depression of conductivity induced by cold. 



Paralysis of Conductivity and Restoration by 

 Tetanising Shock 



In connection with this subject I came across the interest- 

 ing phenomenon of paralysis of conductivity as an after- 

 effect of intense cooling. After obtaining the record of the 



M 2 



