NERVOUS DISCHARGES 19 



ward movement, M2. After repeated experiences the sight of 

 the fire no longer excites a forward movement. 



Let us now pass to the problem of association of ideas. The 

 diagram given here will illustrate it (Figure 003). Ma and 

 Mb represent movements not opposed to each other. 



As before, the channels Sa, Ma and Sb, Mb are of high con- 

 ductivity while the median channel Sa, Sb, x, y, Ma, Mb is 

 originally of low conductivity so that before experience the 

 sensation Sa is followed only by the movement Ma and the 

 sensation Sb is followed only by the movement Mb. Now let 

 the environment be such that the sensation Sa is always suc- 

 ceeded quickly by Sb or vice versa. The discharge through 

 the median channel Sa, Sb, x, y, Ma, Mb will be greater at 

 each experience from our premises as in inhibition so that after 

 a number of experiences the sensation Sa (or Sb) will result in 



Sb Sa 



Ma 



L \ Mb 



Figure 003 



both movements Ma and Mb. Again the weak channel has 

 grown faster and overtaken the strong ones. Eventually the 

 originally weak channel will have dwarfed the others and for 

 either sensation the discharge will be practically equal at Ma 

 and Mb. 



This case we may call one of diverging nervous channels. 

 In it may be found the physiological accompaniment of the 

 association of ideas. 



As an illustration : the crack of the whip (Sa) makes the 

 young horse prick up his ears (Ma) ; the sting of a blow makes 

 him jump forward (Mb). If the blow often follows the sound, 

 the jump will after a while be excited by cracking the whip. 

 The ideas of the sound and the pain have become associated 

 as the psychologist would say. 



Looking at the problem from a quite different point of view 

 for a moment, we may picture our nervous channels as chains 

 or groups of neurons, each neuron being an individual organism. 



