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THE PHYSICAL BASIS OF MIND. 37 



the Association of Ideas. This is the root and branch of the 

 whole structure psychological, and therefore, if mind has a 

 physical basis, we should expect to meet with some very 

 general and essential feature of ganglionic action answering 

 to this very general and essential feature of mental action. 

 And this, beyond question, we do hnd. 



For the association of ideas is merely a development of 

 simple memory. A mental impression, image, memory, or 

 idea having once occurred in juxtaposition with another, not 

 only are the two memories remembered, but also the fact of 

 their juxtaposition, so that when one memory or idea is 

 aroused, the other is aroused likewise. Let us, then, look at 

 the matter a little more closely, in order to see how this great 

 principle of psychology may receive its explanation, so far as 

 the collateral principle of physiology is concerned. 



There can be no doubt that in the complex structure of 

 the cerebral hemispheres one nervous arc {i.e., fibres, cells, 

 and fibres) is connected with another nervous arc, and this 

 with another almost ad infinitum;, and there can be equally 

 little doubt that processes of thought are accompanied by 

 nervous discharges taking place, now in this arc, and now in 

 that one, according as the group of nerve-cells in each arc is 

 excited to discharge its influence by receiving a discharge 

 from some of the other nerve-arcs with wliich it is united. 

 Again, as we have seen, it is practically certain that the 

 more frequently a nervous discharge takes place through a 

 given group of nervous arcs, the more easy will it be for sub- 

 sequent discharges to take place along the same routes — these 

 routes having been thus rendered more permeable to the pas- 

 sage of subsequent discharges. And now a very little reflec- 

 tion will show that in this physiological principle we no 

 doubt have the objective side of the psychological principle 

 of the association of ideas. For it may be granted that a 

 series of discharges taking place through the same group of 

 nervous arcs will always be attended with the occurrence of 

 the same series of ideas ; and it may be further granted that 

 the previous passage of a series of discharges through any 

 group of nervous arcs, by making the route more permeable, 

 will have the eflect of making subsequent discharges pursue 

 the same course when started from the same origin. And if 

 these two propositions be granted, it follows that the tendency 

 of ideas to rec\n in the same order as that in wliich thev 



