248 SENSATION AND THE SENSIFEROUS ORGANS. [LECT. 



questions of pure philosophy are dealt with imme- 

 diately after those of physics. If so, the accident 

 is happily symbolical of the essential relations of 

 things ; for metaphysical speculation follows as closely 

 upon physical theory as black care upon the horse- 

 man. 



One need but mention such fundamental, and 

 indeed indispensable, conceptions of the natural philo- 

 sopher as those of atoms and forces : or that of attrac- 

 tion 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 back- 

 ground of physics and chemistry ; while, in the bio- 

 logical 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 metaphysical fetichisin ? Is the doc- 

 trine of final causes legitimate or illegitimate ? These 

 are a few of the metaphysical topics which are sug- 

 gested 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. No 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 diges- 

 tion ; 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 funda- 

 mental of all metaphysical problems. In fact, the 



