als--and those usually who are of
quickest intelligence--display a somewhat quicker rate of rhythm, which
may be as high as eleven per second. Moreover, it is found that by
stimulating with strychnine any of the centres of reflex action, pretty
nearly the same rate of rhythm is exhibited by the muscles thus thrown
into contraction; so that all the nerve-cells in the body are thus shown
to have in their vibrations pretty nearly the same period, and not to be
able to vibrate with any other. For no matter how rapidly the electrical
shocks are allowed to play upon the grey matter of the cerebral
hemispheres, as distinguished from the nerve-trunks proceeding from them
to the muscles, the muscles always show the same rhythm of about nine
beats per second: the nerve-cells, unlike the nerve-fibres, refuse to
keep time with the electric shocks, and will only respond to them by
vibrating at their own intrinsic rate of nine beats per second.

Thus much, then, for the rate of molecular vibration which goes on in
nerve-centres. But the rate of such vibration which goes on in sensory
and motor nerves may be very much more rapid. For while a nerve-centre
is only able to _originate_ a vibration at the rate of about nine beats
per second, a motor-nerve, as we have already seen, is able to
_transmit_ a vibration of at least 1,000 beats per second; and a sensory
nerve which at the surface of its expansion is able to respond
differently to differences of musical pitch, of temperature, and even of
colour, is probably able to vibrate very much more rapidly even than
this. We are not, indeed, entitled to conclude that the nerves of
special sense vibrate in actual unison, or synchronize, with these
external sources of stimulation; but we are, I think, bound to conclude
that they must vibrate in some numerical proportion to them (else we
should not perceive objective differences in sound, temperature, or
colour); and even this implies that they are probably able to vibrate at
some enormous rate.

With further reference to these molecular movements in sensory nerves,
the following important observation has been made--viz. that there is a
constant ratio between the amount of agitation produced in a sensory
nerve, and the intensity of the corresponding sensation. This ratio is
not a direct one. As Fechner states it, 'Sensation varies, not as the
stimulus, but as the logarithm of the stimulus.' Thus, for instance, if
1,000 candles are all throwing