CONSCIOUSNESS AND SENSATION. 93 
impression is conducted to the seat of consciousness 
in the cerebral hemispheres, corpuscles there enter 
into a corresponding condition to that of the con- 
ducting nerve, precisely as a corpuscle which is the 
turning-point in a reflex action is no doubt affected 
by the condition which it receives from the sensory 
and passes on to the motor nerve. But if we 
imagine that in an act of consciousness the cor- 
puscles of the hemispheres undergo any change 
other than that of passing into the impressed con- 
dition studied in nerves, we become guilty of an 
assumption which has the plain objection of being 
unfounded. That assumption is unfortunately 
often made, apparently from confusion of ideas ; 
for authors, particularly medical authors, speak as 
if mental impressions lodged in the brain ; whereas 
nervous impression, the only active condition into 
which there is evidence of the brain passing, is 
a physical state of a uniform nature, while, on the 
other hand, a mental impression is the presence of 
a notion in the mind, and the variety of such 
notions is infinite. I shall return to the considera- 
tion of the bearing of this remark on views as to 
the details of the functions of the hemispheres, but 
wish first to direct attention to the difficulties of 
the received doctrine of sensation. 
I own that, even supposing all difficulties as to 
