94 HUME 



III 



crudity of his notions and the strangeness of the 

 language in which they are couched, it must in 

 justice be remembered, that what are now known 

 as the elements of the physiology of the nervous 

 system were hardly dreamed of in the first half of 

 the eighteenth century ; and, as a further set off 

 to Hume's credit, it must be noted that he grasped 

 the fundamental truth, that the key to the com- 

 prehension of mental operations lies in the study 

 of the molecular changes of the nervous apparatus 

 by which they are originated. 



Surely no one who is cognisant of the facts of 

 the case, nowadays, doubts that the roots of 

 psychology lie in the physiology of the nervous 

 system. What we call the operations of the mind 

 are functions of the brain, and the materials of 

 consciousness are products of cerebral activity. 

 Cabanis may have made use of crude and mis- 

 leading phraseology when he said that the brain 

 secretes thought as the liver secretes bile ; but 

 the conception which that much-abused phrase 

 embodies is, nevertheless, far more consistent 

 with fact than, the popular notion that the mind 

 is a metaphysical entity seated in the head, but as 

 independent of the brain as a telegraph operator 

 is of his instrument. 



It is hardly necessary to point out that the 

 doctrine just laid down is what is commonly 

 called materialism. In fact, I am not sure that 

 the adjective "crass," which appears to have a 



