INTERFERENCE OF EXCITATIONS 



207 



of occurrence. The disintegration, determined by energy pro- 

 duction, reaches a maximum suddenly, then diminishes, at first 

 rapidly, then more and more slowly until the zero point is reached. 

 In an analogous manner the irritability abruptly reaches a mini- 

 mum, then increases rapidly, then more slowly, until it again 

 reaches its previous value. When we represent these processes 

 by a curve, they assume the following form. (Figure 47.) In 



Fig. 47. 



this diagram the abscissa is the time, the ordinate value zero is 

 the level of the metabolism of rest and the specific irritability. 

 The points above the abscissa represent disintegration, that is, 

 energy production, those under the abscissa, the reduction of irri- 

 tability. A consideration of the latent period may be omitted. 

 At the end of the curve the effect of stimulation may be assumed 

 to have disappeared and the state of metabolic equilibrium re- 

 established. If we base our further observations upon this curve 

 of excitation, we can study in them the factors upon which 

 responsivity is dependent when a second exciting stimulus is 

 operative during the course of the first. 



It is from the beginning apparent that the response to the 

 second stimulus is determined by the intensity of the second 

 stimulus in relation to the degree of irritability which exists at 

 the moment when this is effective. This relation is dependent 

 first upon the absolute intensity of the second stimulus. In the 

 following diagram the intensity of the existing threshold value is 



