PROFESSOR VIRCHOW AND EVOLUTION. 389 



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 ac- 

 knowledge my helplessness. The association 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 mechan- 

 ical connection between the sun and our organs, in 

 the former case logical continuity disappears. Be- 

 tween molecular mechanics and consciousness is inter- 

 posed a fissure over which the ladder of physical reason- 

 ing 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, mani- 

 fests 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 



