208 



IRRITABILITY 



fixed for convenience as ordinates beneath the abscissa. If, for 

 example, at the time point x, a stimulus of weak intensity Ri acts, 

 this stimulus being under the existing threshold, produces no 

 perceptible effect. (Figure 48.) If now instead of a weak stimu- 

 lus, one of stronger intensity acts at the time point x, this stimulus 



Fig. 49. 



will produce an appreciable response. (Figure 49.) If the sec- 

 ond stimulus is of the same strength as the first, this second stimu- 

 lus will bring about relatively less disintegration, because the 

 system is then in a state in which irritability is still reduced. 

 But this lessened disintegration in that it summates the excita- 

 tion still existing as the result of the first stimulus can produce 

 an absolute increase of the height above that of the abscissa. 



