TABLE XXIV.—SHOWING RESPONSIVE EFFECTS COMMON TO PULVINI AND GROWING ORGANS UNDER UNILATERAL STIMULATION.
| Effect of direct stimulation on proximal side. | Effect of indirect stimulation on distal side. |
| Diminution of turgor | Increase of turgor. |
| Galvanometric negativity | Galvanometric positivity. |
| Contraction and concavity | Expansion and convexity. |
| When stimulus is strong or long continued, thetrue excitatory effect is conducted to the distal side, neutralising or reversing the first response. | |
The diagram which I have already given (Fig. 98) clearly explains the different tropic effects induced by changing the point of application of stimulus. We may thus have stimulus applied at the responding region itself (Direct Stimulation) or at some distance from it (Indirect Stimulation). The final effect will be modified by the conducting power of the tissue.
DIRECT UNILATERAL STIMULATION.
Type I.—The tissue has little or no power of transverse conduction: stimulus remains localised, the proximal side undergoes contraction, and the distal side expansion. The result is a positive curvature.
Type II.—The tissue is transversely conducting. Under strong and long continued stimulation the excitatory impulse reaches the distal side, neutralising or reversing the first effect.
INDIRECT UNILATERAL STIMULATION.
Type I.—The intervening tissue is an indifferent conductor: transmitted positive impulse induces expansion and convexity on the same side, thus giving rise to negative curvature (i.e., away from stimulus).
Type II.—Intervening tissue is a fairly good conductor: the effect of positive impulse is over-powered by the predominant excitatory negative impulse, the final result is a concavity and positive curvature, with movement towards the stimulus.