16 S. BENT RUSSELL 



of certain channels more than others. Take the familiar but 

 perplexing case of inhibition of muscular action shown here by 

 diagram. (Figure ooi.) Let Si and S2 be sensations. Mi 

 represents a forward movement, M2 a backward movement. 

 Si, Mi and S2, M2 are channels of good conductivity. The 

 cross channel Si, x, M2 is of low conductivity so that before 

 experience is gotten, sensation Si gives response Mi a forward 

 movement. After experience is had we observe the sensation 

 Si is followed by response M2, a backward movement. We 

 conclude that channel Si, x, M2 has as a result of experience 

 become of high conductivity, exceeding Si, Mi. How can we 

 explain this? How can experience have developed the weak 

 channel and not the strong one? 



S2 SI 



Figure 001 



Now, as to the conductivity of nerves we find evidence to 

 support the following premises: 



1. The effect at the motor end of a nervous channel is not 

 always in proportion to the intensity of the impression at the 

 sensory end. We may state it thus: The susceptibility of a 

 nervous channel is greater at one time than at another or con- 

 versely we may state : The resistance of a channel to nervous 

 discharges is less at one time than at another. The same rule 

 will hold it is believed even though the nerves forming the 

 channel considered be perfectly normal as to nourishment ; that 

 is to say that normally nourished nerves are of variable sus- 

 ceptibility. 



2. The first discharge through a channel after a period of 

 rest will increase the susceptibility. If the impression at the 

 sensory end is repeated at proper short intervals the suscepti- 

 bility will be steadily increased. 2 



2 Spencer, Herbert. Principles of Psychology. New York, 1894, pp. 577, 614. 

 Thorndike, E. L. Animal Intelligence. New York, 1911, p. 267. 



