CYCLIC MOLECULAR VARIATION 



639 



In (b) is seen the reversal of the normal electro-motive 

 response in the digesting leaf of Drosera, after tetanisation, 

 the stimulus here also being electrical. In (c] we have 

 reversal after tetanisation in the elec- 

 tro-motive response of the pulvinus 

 of Mimosa. And in (d} is given a 

 similar reversal after tetanisation, in 

 the response of tungsten powder, the 

 record being here of the resistivity 

 variation, under the stimulus of 

 Hertzian radiation. These, and other 

 results already given, have been 

 obtained by the employment of 

 different forms of stimulation. We 

 may, therefore, regard these charac- 

 teristic transformations as brought 

 about by all forms of stimulus alike. 

 We thus see that one identical 

 stimulus may give rise to opposite 

 effects, according to the molecular 

 condition of the responding tissue. 

 This molecular transformation, more- 

 over, may be brought about by the 

 previous action of the stimulus itself. 

 These considerations will, I think, be 

 found to elucidate the very obscure 

 question of the effect of drugs, with 

 special reference to the opposite 

 actions of large and small doses. 

 Since a chemical substance acts in 

 a manner not unlike that of other 

 stimulating agents, a moderate dose 

 of a given reagent might be expected 

 to induce effects similar to that of 

 the action of moderate stimulation, 

 inducing molecular transformation will generally be to en- 

 hance excitability, as from B to C. Too long-continued action, 



FIG. 396. Series showing 

 reversal of Normal Re- 

 sponse by fatigue due to 

 strong Tetanisation in- 

 ducing the E phase 



a, Mechanical response of 

 frog's nerve ; b, Electro- 

 motive response of Dro- 

 sera ; c, electro -motive 

 response of pulvinus of 

 Mimosa ; </, Response 

 by resistivity variation 

 of tungsten powder. 



Hence its effect in 



