On the Vital Principle/Book 2/Prelude to Chapter 5
Prelude to Chapter V.
Aristotle, having fully inquired into the process of nutrition, here enters upon the investigation of the sensibility or sentient system, which is, as he said, the line of separation between animal and vegetable existence; the inquiry includes, of course, the senses and their organs, as well as allusions to those external forces or qualities which by their action produce simultaneous perception, that is, sensation. Sensibility is one of the great mysteries of our mortal nature, but its investigation was, in that age, additionally complicated and abstruse, as the brain as well as its relation to the spinal cord and connexion with the organs of the senses were unknown. But, although anatomy has detected the links between the brain and sentient organs, and thus shewn that the senses are emanations, so to say, from it, yet this knowledge, however otherwise valuable, does not explain how matter has been constituted thus to produce sensation, and, by reflexion, consciousness.