CHAPTER III 



METHODS OF STIMULATION 



Different methods of stimulating the plant : mechanical, chemical, thermal, 

 and electrical — Difficulties of securing quantitative stimuli — Direct 

 and indirect stimulation — Ideal modes of stimulation — Electro- 

 thermic stimulation — Stimulation by constant current — Stimulation 

 by condenser-discharge — Non-polarisable electrodes — Direct, extra- 

 electrodal, and intra-electrodal stimulation — Stimulation by induction 

 shock — Effects of make- and break-shock — Excitation by tetanising 

 shock. 



In the case of contractile animal muscle, various stimuli 

 give rise to excitation, and it is a very remarkable fact that 

 the same stimuli exercise a similar excitatory influence 

 on the pulvinus of Mimosa. Classifying these stimuli, 

 we find that they are : — 



1. Mechanical. — A blow will excite animal muscle and 

 cause mechanical response. A similar effect is induced by 

 a mechanical blow in the pulvinus of Mimosa. A prick or 

 cut also will cause contraction in either. 



2. Chemical. — Various chemical agents are found to 

 induce excitation in botl* animal and vegetal contractile 

 tissues. Thus dilute hydrochloric acid or ammonia causes 

 excitation of both muscle and pulvinus. 



3. Thermal. — The application of a hot wire will induce 

 responsive contraction in both cases. 



4. Electrical. — The muscle may be excited by an induc- 

 tion-shock. The pulvinus of Mimosa is also excited by 

 such shocks. Other modes of electrical stimulation, such 

 as that of condenser-discharge and that of the applica- 

 tion of a constant electrical current, are found effective in 

 causing excitation of animal tissues. It will be seen in the 



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