THE NERVOUS SYSTEM. 467 



tuatomical probability, we may venture to observe, that these hypo- 

 theses do not tend at all to elucidate the physiological principle which 

 is here involved ; for this principle cannot be mechanical, chemical, o> 

 physical, and therefore cannot be better understood by embodying it 

 in a fluid ; the difficulty we have in conceiving what the moving force 

 is, is not got rid of by explaining the machinery by which it is merely 

 transferred. In tracing the phenomena of sensation and volition to 

 their cause, it is clear that we must call in some peculiar and hyper- 

 physical principle. The hypothesis of a fluid is not made more satis- 

 factory by attenuating the fluid ; it becomes subtle, spirituous, ethereal, 

 imponderable, to no purpose; it must cease to be a fluid, before its 

 motions can become sensation and volition. This, indeed, is acknow- 

 ledged by most physiologists ; and strongly stated by Cuvier. 19 " The 

 impression of external objects upon the ME, the production of a sensa- 

 tion, of an image, is a mystery impenetrable for our thoughts." And 

 in several places, by the use of this peculiar phrase, " the me" (le moi,} 

 for the sentient and volent faculty, he marks, with peculiar appropri- 

 ateness and force, that phraseology borrowed from the world of matter 

 will, in this subject, no longer answer our purpose. We have here to 

 :i'o from Nouns to Pronouns, from Things to Persons. We pass from 

 the Body to the Soul, from Physics to Metaphysics. We are come to 

 the borders of material philosophy ; the next step is into the domain 

 of Thought and Mind. Here, therefore, we begin to feel that we have 

 reached the boundaries of our present subject. The examination of 

 that which lies beyond them must be reserved for a philosophy of 

 another kind, and for the labors of the future ; if we are ever enabled 

 to make the attempt to extend into that loftier and wider scene, the 

 principles which we gather on the ground we are now laboriously 

 treacling. 



Such speculations as I have quoted respecting the nervous fluid, pro- 

 ceeding from some of the greatest philosophers who ever lived, prove 

 only that hitherto the endeavor to comprehend the mystery of percep- 

 tion and will, of life and thought, have been fruitless and vain. Many 

 anatomical truths have been discovered, but, so far as our survey has 

 yet gone, no genuine physiological principle. All the trains of physiolo- 

 gical research which we have followed have begun in exact examination 

 of organization and function, and have ended in wide conjectures and 

 arbitrary hypotheses. The stream of knowledge in all such cases is 



19 Regne Animal, In trod. p. 47. 



