V ANIMAL AUTOMATISM 239 



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 affections 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 impres- 

 sion leaves behind a record in the structure of the 

 brain an " ideagenous " molecule, so to speak, 

 which is competent, under certain conditions, to 

 reproduce, in a fainter condition, the state of con- 

 sciousness which corresponds with that sensory 

 impression ; and it is these " ideagenous mole- 

 cules " which are the physical basis of memory. 



It may be assumed, then, that molecular 

 changes in the brain are the causes of all the 



