EFFECT OF STIMULUS ON TONIC CONDITION I49 



(1) The specimen was in an ordinary condition, and the 

 stimulus applied was strong and long-continued. The 

 D change was found to be greater than the A (A < D). At 

 the end of the operation the tonic condition fell below the 

 former level, as evidenced by the responses exhibiting 

 fatigue depression. 



(2) The specimen was in a sub-tonic condition, as shown 

 by the feeble character of the response. Stimulus stirred 

 up the relatively inert tissue to activity, and the up-change 

 A was greater than the down-change D (A > D). The 

 tonicity was now found to have been raised by stimulus 

 above the former level, as shown by a marked enhancement 

 of the response. Other instances of this are met with in the 

 so-called ' staircase effect,' where uniform stimuli evoke 

 responses which undergo a continuous increase. 



(3) An intermediate type was found in which successive 

 stimulations of moderate intensity applied to vigorous 

 specimens gave rise to uniform responses. The tonic condi- 

 tion remained unchanged, the A and D changes being equal 

 (A = D). 



Thus two diametrically opposite effects are produced in 

 responding tissues the tonic condition of which is above 

 or below par. In highly excitable tissues response undergoes 

 diminution under strong stimulus, while in sub-tonic tissues 

 it exhibits enhancement. 



(b) Effects parallel to these are found in the autono- 

 mous activities of the plant. Strong stimulus inhibits the 

 vigorous pulsation of the leaflets of Desmodium gyrans ; in 

 relatively inactive specimens, where the pulsation is feeble 

 or at a standstill, stimulus enhances or renews it. In growth 

 also the rate is depressed in active specimens under the 

 action of stimulus ; but in specimens with feeble growth, 

 moderate stimulus enhances the rate. 



