SENSATION AND THE SENSIFEROUS ORGANS. 255 



tions of pure philosophy are dealt with immediately 

 after those of physics. If so, the accident is happily 

 symbolical of the essential relations of things ; for meta- 

 physical speculation follows as closely upon physical 

 theory as black care upon the horseman. 



One need but mention such fundamental, and in- 

 deed indispensable, conceptions of the natural philoso- 

 pher as those of atoms and forces : or that of attraction 

 considered as action at a distance ; or that of potential 

 energy ; or the antinomies of a vacuum and a plenum ; 

 to call to mind the metaphysical background of physics 

 and chemistry ; while, in the biological sciences, the 

 case is still worse. "What is an individual among the 

 lower plants and animals? Are genera and species 

 realities or abstractions ? Is there such a thing as Vital 

 Force ? or does the name denote a mere relic of meta- 

 physical fetichism ? Is the doctrine of final causes 

 legitimate or illegitimate? These are a few of the 

 metaphysical topics which are suggested by the most 

 elementary study of biological facts. But, more than 

 this, it may be truly said that the roots of every system 

 of philosophy lie deep among the facts of physiology. 

 Xo one can doubt that the organs and the functions 

 of sensation are as much a part of the province of 

 the physiologist, as are the organs and functions of 

 motion, or those of digestion ; and yet it is impossible 

 to gain an acquaintance with even the rudiments of 

 the physiology of sensation without being led straight 

 to one of the most fundamental of all metaphysical 



