210 LIFE AND WORK OF SIR JAGADIS C. BOSE 



inquiry, though to others less satisfactory. According 

 to this, the strength of stimulus must be increased 

 in geometrical ratio, in order that the intensity ol 

 psycho-physiological reaction may increase arithmetically. 

 According to Weber's Law the relation between stimulus 

 and response is quantitative ; it does not take into account 

 that the quality or sign of response is also liable to change. 

 But Bose's experiments have here yielded significant results. 

 Their many records of living tissues bring out the striking 

 fact that the sign of response is modified by the strength 

 of stimulus. Hence the relation between stimulus and 

 response is by no means so simple as Weber, Fechner, and 

 their successors have assumed ; for tracings obtained with 

 Bose's finer recording instruments show that what seemed 

 formerly a subminimal stimulus may really produce 

 appreciable effects. Moreover, a very feeble stimulus gives 

 a distinct response of positive sign, i.e. expansion the 

 very opposite to the contractile response under usual 

 stimulation. The continuance or even moderate increase 

 of the feeble stimulus shows a diminishing result, going back 

 to a point of no apparent response at all. Yet this is not 

 a true zero, but a balance of opposite responses ; for with 

 a continued increase of stimulus the opposite and usual 

 response begins, and increases to its maximum, as Weber 

 observes. The fresh observation just noted introduces an 

 element of qualitative transformation previously unsus- 

 pected, and in fact overlooked. 



By employing very delicate methods of mechanical 

 and electrical response, Bose discovered two distinct 

 impulses of opposite signs which occur in the conducting 

 nerve according to whether the stimulation be feeble or 

 intense. A feeble stimulus applied at some distance 

 from the responding pulvinus of Mimosa (which acts like 

 contractile muscle) gives rise to an impulse which causes 

 a positive or expansive reaction, by which the leaf becomes 

 erected. A strong stimulus, on the other hand, gives rise 

 to an impulse which induces precisely the opposite reaction 



