INTERFERENCE OF EXCITATIONS 



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more close analysis, nevertheless, we are in a position to attribute 

 to them the origins of summation and inhibitory processes, which 

 occur in all living systems, especially the nervous system. 



For the analysis of summation and the inhibitory processes 

 which occur in the physiologically active organisms or which are 

 experimentally produced, a very important point should be ob- 

 served, that is, the fact that the stimuli which bring about these 

 phenomena are practically always a series of single stimuli. The 

 nerve impulses, for example, consist of a shorter or a longer 

 series of single discharges which follow each other in rapid 

 rhythmic sequence. Here, then, we have the conditions neces- 

 sary for the production of interference effects when these single 

 stimuli follow each other with sufficient frequency and also when 

 there is the combined action of two series. 



Fig. 53. 



Curve showing tlie general development of the effect produced by interference of the 

 stimuli of the same series in an heterobolic system. The effect is first summation 

 and then inhibition. R indicates the intensity of the stimuli, S the level of the 

 threshold of perceptible effect. 



We will first direct our attention to the simplest case brought 

 about by an interference between the individual effects of stimuli 

 in the same series. We will study the effect, which here occurs, 

 in the accompanying diagram, which shows the facts involved in 

 the interference of two stimuli of a series of stimuli. (Figure 

 53.) The curve shows the development of summation and inhi- 

 bition. The single stimuli of equal intensity follow at the same 

 intervals, so that the succeeding stimuli meet with an incomplete 



