138 RESPONSE IN THE LIVING AND NON-LIVING 



of observations for an entire cycle, that is to say, a 

 series of observations were taken for maximum effects, 

 starting from amplitude of vibration of 10 and ending 

 in 100, and backwards from 100 to 10. Effect of 

 hysteresis is very clearly seen (see A, fig. 87) ; there 

 is a considerable divergence between the forward and 

 return curves, the return curve being higher. On re- 

 peating the cycle several times, the divergence is found 

 very much reduced, the wire on the whole is found to 

 assume a more constant sensitiveness. In this steady 

 condition, generally speaking, the sensitiveness for 

 smaller amplitude of vibration is found to be greater 

 than at the very beginning, but the reverse is the case 

 for stronger intensity of stimulation. 



Effect of annealing. I repeated the experiment with 

 the same wire, after pouring hot water into the cell and 

 allowing it to cool to the old temperature. From the 

 cyclic curve (B, fig. 87) it will be seen (1) that the sen- 

 sitiveness has become very much enhanced ; (2) that 

 there is relatively less divergence between the forward 

 and return curves. Even this divergence practically 

 disappeared at the third cycle, when the forward and 

 backward curves coincided (c, fig. 87). The above 

 results show in what manner the excitability of the wire 

 is enhanced by purely physical means. 



It is very curious to notice that addition of Na 2 CO 3 

 solution (see Chap. XV Action of Stimulants) produces 

 enhancement of responsive power similar to that pro- 

 duced by annealing ; that is to say, not only is there a 

 great increase of sensitiveness, but there is also a 

 reduction of hysteresis. 



