98 CONSCIOUSNESS AND SENSATION. 
and suppose them to exist in the fibres of the cord 
alone, we assume that the work which requires a 
whole fibre in a peripheral nerve, can be done by 
one of a multitude of strie in a fibre of the cord, 
which seems improbable. 
If the difficulties which have been enumerated 
appear great, when the received theory is applied 
to the explanation of common sensation, they are 
still more striking when it is applied to vision. 
The theory demands that for every ray of light 
appreciated by the mind there must be a com- 
pletely distinct communication from one of the rods 
or cones which constitute the individual sensory 
organs of the retina to a terminus in the brain, 
and that the impressed condition of every such 
terminus must be capable of creating in the mind 
a knowledge of the position of the point on which 
the ray falls as related to all the other impressed 
points of the retina. That supposition involves 
all the difficulty which has been pointed out in the 
case of common sensation ; while the anatomy of 
the retina, even more distinctly than that of the 
spinal cord, contradicts the possibility of distinct 
communication between each of the immense num- 
ber of peripheral nerve-terminations and the seat of 
consciousness. Within the retina, the threads 
leading from the terminal rods and cones already 
