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 both 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 induction-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 application of a constant electrical current, are found effective in causing excitation of animal tissues. It will be seen in the
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