CHAPTER XVII 



EFFECT OF TEMPERATURE ON POLAR EXCITATION, AND^ 

 MULTIPLE EXCITATION UNDER CONSTANT CURRENT 



Excitability of conducting tissue to induction-shock diminished by cooling — 

 Nerve-excitation by constant current enhanced by cooling — Excitation 

 of conducting-tissue of Mimosa by constant current enhanced by 

 cooling and depressed by warming — Ineffective stimulus becoming 

 effective under cooling and vice versa — Multiple response induced 

 in Biophytum by the passage of constant current — Comparison of 

 sensitiveness of plant and animal — Minimum current for excitation 

 of human tongue — Relatively higher sensitiveness of Biophytum. 



In continuing the investigation on polar reaction, certain 

 modifications of effect were noticed as the season advanced 

 from spring to summer. Some of these will be described in 

 a succeeding chapter. But one modifying effect — namely, 

 that due to temperature — appeared at first very puzzling. 



The temperature of Calcutta in summer is high. More- 

 over experiments with plants had to be carried out in a 

 glass-house. Thus the temperature to which the plants were 

 subjected in summer was often as high as 35 C. In these 

 circumstances it was found that the indirect stimulation of 

 the pulvinus of Mimosa by the action of constant current 

 often became ineffective. It was quite easy in spring to 

 excite the leaf of Mimosa by the transmitted excitation due 

 to the make of kathode when the kathodic point was at a 

 distance of several centimetres from the pulvinus. But in 

 summer there was hardly any transmitted excitation even 

 when the exciting kathode was at a comparatively short 

 distance from the pulvinus. 



This ineffectiveness might be due to the impairment of 

 conductivity or excitability. It could not be due to the 



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