PROFESSOR VIRCHOW AND EVOLUTION. 391 



in mechanical science come to an end ; and if asked 

 to deduce from the physical interaction of the brain 

 molecules the least of the phenomena of sensation or 

 thought, I acknowledge my helplessness. The associ- 

 ation of both with the matter of the brain may be 

 as certain as the association of light with the rising 

 of the sun. But whereas in the latter case we have 

 unbroken mechanical connection between the sun and 

 our organs, in the former case logical continuity dis- 

 appears. Between molecular mechanics and conscious- 

 ness is interposed a fissure over which the ladder of 

 physical reasoning is incompetent to carry us. We 

 must, therefore, accept the observed association as an 

 empirical fact, without being able to bring it under the 

 yoke of a priori deduction. 



Such were the ponderings which ran habitually 

 through my mind in the days of my scientific youth. 

 They illustrate two things a determination to push 

 physical considerations to their utmost legitimate limit ; 

 and an acknowledgment that physical considerations 

 do not lead to the final explanation of all that we feel 

 and know. This acknowledgment, be it said in passing, 

 was by no means made with the view of providing room 

 for the play of considerations other than physical. The 

 same intellectual duality, if I may use the phrase, 

 manifests itself in the following extract from an article 

 entitled ' Physics and Metaphysics,' published in the 

 'Saturday Review ' for August 4, 1860: 



' The philosophy of the future will assuredly take 

 more account than that of the past of the dependence 

 of thought and feeling on physical processes ; and it 

 may be that the qualities of the mind will be studied 

 through organic combinations as we now study the 

 character of a force through the affections of ordinary 



