CHAPTER XXXIV 



EFFECT OF TEMPERATURE AND AFTER-EFFECTS 

 OF STIMULUS ON CONDUCTIVITY 



Effect of temperature in inducing variations of conductivity : (a) by Method of 

 Mechanical Response ; (b] by Method of Electric Balance Effect of cold 

 Effect of rising temperature The Thermal Cell After-effect of stimulation 

 on conductivity The Avalanche Theory Determination of the after-effect 

 of stimulus on conductivity by the Electrical Balance After-effect of moder- 

 ate stimulation After-effect of excessive stimulation. 



IN studying the effect of temperature in inducing variations 

 of conductivity, we may use either of two different methods 

 in the first place the method of mechanical, or in the second 

 that of electrical response. For the first of these it is neces- 

 sary to have what is generally known as a * sensitive ' plant, 

 the leaves or leaflets of which afford conspicuous motile 

 indications of the arrival of the excitatory wave from 

 a distance. In such a case the time-interval between the 

 application of stimulus and the response of a leaflet at a 

 known distance gives us a measure of the velocity of con- 

 duction ; and if we carry out successive experiments at 

 different temperatures we have a means of determining the 

 effect of temperature on conductivity. Employing this 

 method, I have elsewhere given a determination of the 

 effect of temperature on the velocity of transmission in 

 Biophytum sensitivum. It was there shown that lower- 

 ing of temperature reduced the velocity of transmission 

 even to the extent of abolition, when the cooling was suf- 

 ficiently intense. With moderate cooling the velocity was 

 found to be decreased to about one-third. The effect of 

 rise of temperature was, on the contrary, an increase of 



K K 



