ANIMAL INTELLIGENCE. 217 



ceive that all it requires for its manifestation is an incoming nerve, a 

 nerve-centre, and an outgoing nerve, which together constitute what 

 has been called a nervous arc. Now, there can be no reasonable doubt 

 that in the complex structure of the brain one nervous arc is connected 

 with another nervous arc, and this with another almost ad infinitum y 

 and there can be equally little doubt that processes of thought are ac- 

 companied by nervous discharges taking place now in this arc and now 

 in that one, according as the nerve-centre in each arc is excited to dis- 

 charge its influence by receiving a discharge from some of the other 

 nerve-arcs with which it is connected. Again, it is almost certain that 

 the more frequently a nervous discharge takes place through a given 

 group of nervous arcs, the more easy will it be for subsequent discharges 

 to take place along the same routes — these routes having been thus 

 rendered more permeable to the passage of subsequent discharges. So 

 that in this physiological principle of reflex action 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 same 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 efi'ect of making subsequent discharges pursue the same course when 

 started from the same origin. And, if these two propositions be grant- 

 ed, it follows that the tendency of ideas to recur in the same order as 

 that in which they have previously occurred is merely a psychological 

 expression of the physiological fact that lines of reflex discharge become 

 more and more permeable by use. We thus see that the most funda- 

 mental of psychological principles — the association of ideas — is merely 

 an obverse expression of the most fundamental neurological principles 

 — reflex action. But here we have an important qualification to take 

 into account. All reflex action, or neurosis, is not attended with idea- 

 tion, or psychosis. In our own organization, for instance, it is only 

 cerebral reflexes which are so attended ; and even among cerebral re- 

 flexes there is good reason to believe that the greater number of them 

 are not accompanied by conscious ideation ; for analysis shows that it 

 is only those cerebral discharges which have taken place comparatively 

 seldom, and the passage of which is therefore comparatively slow, that 

 are accompanied by any ideas, or changes of consciousness. The more 

 habitual any action becomes, the less conscious do we require to be of 

 its performance ; it is, as we say, performed automatically, or without 

 thought. Now, it is of great importance thus to observe that conscious- 

 ness only emerges when cerebral reflexes are flowing along compara- 

 tively unaccustomed channels, and therefore that cerebral discharges 

 which at first were accompanied by definite ideas may, by frequent 

 repetition, cease to be accompanied by any ideas. It is of importance 

 to observe this fact, because it serves to explain the origin of a number 



