242 ANIMAL AUTOMATISM. 



alism," or of the doctrine of "Pre-established Har- 

 mony " (if any such now exist), must admit that we 

 'have as much reason for regarding the mode of motion 

 of the nervous system as the cause of the state of con- 

 sciousness, as we have for regarding any event as the 

 cause of another. How the one phenomenon causes the 

 other we know, as much or as little, as in any other case 

 of causation ; but we have as much right to believe that 

 the sensation is an effect of the molecular change, as we 

 have to believe that motion is an effect of impact ; and 

 there is as much propriety in saying that the brain 

 evolves sensation, as there is in saying that an iron rod, 

 when hammered, evolves heat. 



As I have endeavoured to show, we are justified in 

 supposing that something analogous to what happens in 

 ourselves takes place in the brutes, and that the affec- 

 tions of their sensory nerves give rise to molecular 

 changes in the brain, which again give rise to, or evolve, 

 the corresponding states of consciousness. Nor can there 

 be any reasonable doubt that the emotions of brutes, and 

 such ideas as they possess, are similarly dependent upon 

 molecular brain changes. Each sensory impression leaves 

 behind a record in the structure of the brain an " idea- 

 genous" molecule, so to speak, which is competent, un- 

 der certain conditions, to reproduce, in a fainter condi- 

 tion, the state of consciousness which corresponds with 

 that sensory impression ; and it is these " ideagenous 

 molecules" which are the physical basis of memory. 



It may be assumed, then, that molecular changes in 



