IX.] ANIMAL AUTOMATISM. 235 



the mode of motion of the nervous system as the cause 

 of the state of consciousness, 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 impression 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 impres- 

 sion ; and it is these " ideagenous molecules " which 

 are the physical basis of memory. 



It may be assumed, then, that molecular changes 

 in the brain are the causes of all the states of con- 

 sciousness of brutes. Is there any evidence that these 

 states of consciousness may, conversely, cause those 



