253 
of Edinhurgli, Session 1883-84. 
of the cold body applied to the horny tip of the finger, and to the 
thin skin covering the sides. The nerve-endings are stimulated by 
the addition or ^vithdrawal of heat from the nerves of the skin. 
This is gradual, and does not correspond to the application of the 
cold body to the surface because of the horny epithelial covering. 
Where this covering is thin, the limitation in time of the sensa- 
tion is more definite than where it is thick ; and could we apply 
the cold body directly to the nerve end-organ, the limits would then 
be very sharply defined. Cover the hand with a glove, and the 
limits would be very ill-defined indeed. 
Sufficient evidence has, I think, been adduced to show, that 
where the limits of a sensation are not well defined in time, we 
may conclude that this is not due to anything in the nature of the 
sensorium, but depends upon the way the external energy is changed 
into nerve energy in the terminal end-organ. 
Let me define a sensation as the result of a transformation of the 
energy travelling along a nerve of sensation from without, into the 
energy manifested by the nerve cell to which it passes. We have, 
I insist, no reason to doubt that if that nerve energy travelled 
twenty times a second along a nerve of smell, of taste, hearing, 
or of sight, we should be conscious of twenty separate sensations 
in each case. 
That such a transmission is impossible in every case we know, 
but it is due to the fact that in these cases the nerve cannot be 
stimulated from without so frequently. 
In the case of the ear, the limits in time of high notes are sharper 
than those of the low notes, and probably this is due to a better 
damping apparatus in the ear. Could we increase the perfection of 
this damping, the limits of the consciousness in hearing would 
probably be sharpened almost indefinitely, for we must remember 
that the cause of the different sensations of sound is a difference of 
pitch, or periods of stimulation recurrent in time to which the sen- 
sorium is extremely sensitive. 
If this be true, the period of time taken by a stimulus to produce 
a sensation depending upon the time taken by its energy to be 
transformed into nerve energy in the peripheral end-organ, will be 
some indication of the manner of this transformation. For instance, 
there is a very marked interval between the moment at which the 
