CONSCIOUSNESS AND SENSATION. 107 
existence of distinct routes, as has hitherto been 
done. 
Let it be distinctly understood that I do not say 
that consciousness resides in the nerve-extremities, 
but only that when the nerves are in the active or 
impressed condition in their whole extent up to 
the brain, the consciousness is affected directly 
by the irritations applied to their extremities. 
The relation then of consciousness to the brain 
remains totally different from its relation to the 
nerve. The impressed condition of the cerebral 
corpuscles produces only excitement of the mind ; 
the impressed condition of a peripheral nerve or 
its extremity continued up to the brain brings 
the consciousness into communication with the 
irritation applied. 
At the extremities of the different nerves are 
placed various arrangements which are least com- 
plicated in the nerves of general sense, and which 
modify their capability of being irritated by differ- 
ent stimuli, Thus the expansion of the optic 
nerve is incapable of being affected by the irritation 
of light, but the rods and cones of the retina are 
irritated by them with ease. The complicated 
nerve-extremities of the ear are acted on by sounds, 
and the comparatively simple extremities of the 
nerves of general sense are acted on by mechanical 
