32 FUNCTIONAL INERTIA 



"The effect of applying a stimulus to the cell is 

 to increase the metabolic processes. In order that 

 those excitatory processes may prevail against the 

 inhibitory, it is necessary that they should attain 

 a certain superiority above the latter. As soon as 

 this condition is reached the excitatory processes 

 break through the resistance of the inhibitory, and 

 an explosive discharge is the result. After the 

 discharge, the inhibitory processes are in the ascen- 

 dant, and the stimulus from without has to continue 

 acting for a further length of time before the excita- 

 tion can gather fresh strength to break again through 

 the resistance. This speculation, in default of a 

 better, has played a great part in the speculations 

 of physiologists on the nature of inhibition and the 

 production of rhythmic activity. It suffers, however, 

 as was pointed out by Gad, from the drawback that 

 the molecular processes have to be considered as 

 endowed with inertia, otherwise * as soon as the 

 excitatory are in excess of the inhibitory processes, 

 there would be a leaking discharge, and a constant 

 stimulus would cause a constant activity." 



Later in the chapter (p. 292) Professor Starling 

 writes : " Under normal conditions this constant 

 stimulation may be afforded by : 



fc (i) The sum of afferent impulses arriving at the 

 centre. 



"(2) The venosity of the circulating blood. 



" (3) The normal metabolic change in the nerve- 

 cells." 



* Italics are mine. 



