74 Darwinism and Other Essays. 



of heat, or that friction-electricity is a product of 

 sensible motion. Instead of entering into the dy- 

 namic circuit of correlated physical motions, the 

 phenomena of consciousness stand outside as ut- 

 terly alien and disparate phenomena. They stand 

 outside, but uniformly parallel to that segment 

 of the circuit which consists of neural undula- 

 tions. The relation between what goes on in con- 

 sciousness and what goes on simultaneously in the 

 nervous system may best be described as a re- 

 lation of uniform concomitance. I agree with 

 Professor Huxley and Mr. Harrison that along 

 with every act of consciousness there goes a mo- 

 lecular change in the substance of the brain, in- 

 volving a waste of tissue. This is not materialism, 

 nor does it alter a whit the position in which we 

 were left by common sense before nervous physi- 

 ology was ever heard of. Everybody knows that, 

 so long as we live on the earth, the activity of 

 mind as a whole is accompanied by the activity 

 of brain as a whole. What nervous physiology 

 teaches is simply that each particular mental act 

 is accompanied by a particular cerebral act. In 

 proving this, the two sets of phenomena, mental 

 and physical, are reduced each to its lowest terms, 

 but not a step is taken toward confounding the 

 one set with the other. On the contrary, the 



