INTRODUCTION. ix 



ence is made to the doctrine of sensation put 

 forward in the memoir " On the Physical Relations 

 of Consciousness and the Seat of Sensation." That 

 doctrine may not have received much attention ; 

 but it is in the position of remaining unassailed, 

 while the old doctrine is unsatisfactory to some of the 

 most competent judges, and remains undefended 

 from the objections here brought against it. 



With regard to the fifth article of the series, it 

 need only be said that the connection of the theory 

 of cell-life with that of life in every other aspect is 

 too close to require more than mention here ; while 

 to one who believes in life within life and in the 

 unity of cause in the order of events in each, cell-life 

 is especially interesting as the simplest of a series of 

 which the most complex known is the life-evolution 

 on the face of the earth. 



Every one is familiar by this time with the re- 

 luctance of certain physicists and naturalists to take 

 into consideration even the possibility of such an 

 element as spirit being necessary for the construc- 

 tion of a rational philosophy of nature. The 

 wonderful advances in physics, affording sure foot- 

 ing for further progress within that domain, and 

 giving play for speculations formerly inconceivable, 

 may lead some physicists to overleap those strict 

 fences the observance of which has secured the ad- 

 vance of their favourite studies, and they may 

 dream that the physical is the only world. So also 



