GENERAL SURVEY 355 



independently by means of mechanical and electric 

 responses. 



Two diametrically opposite effects are thus induced by 

 an identical stimulus, depending on direct or indirect appli- 

 cation. The existence of the positive or the indirect effect 

 of stimulus has hitherto been unsuspected. It must be 

 taken into full consideration in unravelling the complexities 

 of reaction in a responding organ. 



The laws of direct and indirect effects of stimulus 

 are : 



The effect at the responding region of a strong excitation 

 transmitted through a short distance or through a good 

 conducting channel, is negative, being the same as the 

 effect under direct stimulation. The response is by negative 

 turgidity-variation, contraction, fall of leaf, and electrical 

 change of galvanometric negativity. This is the direct 

 effect of stimulus. 



The effect of feeble stimulus transmitted through a 

 great distance or through a semi-conducting channel, is 

 positive. The responsive reaction is by positive turgidity- 

 variation, expansion, erection of leaf, and electrical change 

 of galvanometric positivity. This is the indirect effect of 

 stimulus. 



Multiple Response 



In taking records of electric response it is often found 

 that, while a single moderate stimulus gives rise to a single 

 response, a strong stimulus gives rise to a multiple series 

 of responses. Similarly in Biophytum and Averrhoa, while 

 a moderate stimulus gives rise to a single mechanical 

 response, a strong stimulus gives rise to a multiple series 

 of responses. These multiple responses are induced by 

 various modes of strong stimulation, such as induction 

 shock, constant current, strong light, thermal shock, and 

 chemical excitation (p. 285). 



When Biophytum is subjected to successive stimuli 



