108 CONSCIOUSNESS AND SENSATION. 
irritations and changes of temperature. It appears 
then that if we suppose that the consciousness is 
directly affected by the application of the irritation 
to the nerve-extremity, we have the simplest pos- 
sible explanation of differences of colour and of 
notes, and of the different kinds of sensation, con- 
veyed by the nerves of general sense. We are in 
a position to say that as the irritation varies so 
varies the sensation, without being obliged to 
assume different kinds or conditions of nerves 
without evidence. 
The objections may be urged against my theory 
that irritation of the ulnar nerve produces sensation 
in the finger ends, that persons after amputation of 
an arm feel pain in the fingers, and that irritation 
of one nerve often causes pain in another, as when 
disease of the hip gives pain in the knee, or tooth- 
ache pain in the temple; but it appears to me that 
all these things are better explained by this theory 
than by the received one. When one strikes the 
ulnar nerve at the elbow accidentally with force 
everybody knows that the acute pain is not felt 
in the fingers, but at the part struck, and that this 
is immediately succeeded by pain and a peculiar 
sense of vibration which travel downwards from 
the struck part till they reach the fingers. A 
patient who has had a limb removed, in like 
