PROFESSOR VIRCHOW AND EVOLUTION 427 



which, strictly interpreted, is atomic motion, is, in such 

 a case, propagated along the nerve, and communicated to 

 the brain. Again, on feeling the sting I flap the insect 

 violently away. What has caused this motion of my hand ? 

 The command from the brain to remove the insect travels 

 along the motor nerves to the proper muscles, and, their 

 force being unlocked, they perform the work demanded 

 of them. But what moved the nerve molecules which 

 unlocked the muscle ? The sense of pain, it may be re- 

 plied. But how can a sense of pain, or any other state 

 of consciousness, make matter move ? Not all the sense of 

 pain or pleasure in the world could lift a stone or move 

 a billiard-ball; why should it stir a molecule? Try to 

 express the motion numerically in terms of the sensation, 

 and the difficulty immediately appears. Hence the idea 

 long ago entertained by philosophers, but lately brought 

 into special prominence, that the physical processes are 

 complete in themselves, and would go on just as they do 

 if consciousness were not at all implicated. Conscious- 

 ness, on this view, is a kind of by-product inexpressible 

 in terms of force and motion, and unessential to the mo- 

 lecular changes going on in the brain. 



Four years ago, I wrote thus: "Do states of conscious- 

 ness enter as links into the chain of antecedents and se- 

 quence, which gives rise to bodily actions ? Speaking for 

 myself, it is certain that I have no power of imagining 

 such states interposed between the molecules of the brain, 

 and influencing the transference of motion among the 

 molecules. The thing 'eludes all mental presentation.' 

 Hence an iron strength seems to belong to the logic which 

 claims for the brain an automatic action uninfluenced by 

 consciousness. But it is, I believe, admitted by those who 



