is system, and which are concerned in all the
processes of reflex adjustment, sensation, perception, emotion,
instinct, thought, and volition.

First of all, the rate at which these molecular movements travel through
a nerve has been measured, and found to be about 100 feet per second, or
somewhat more than a mile a minute, in the nerves of a frog. In the
nerves of a mammal it is just about twice as fast; so that if London
were connected with New York by means of a mammalian nerve instead of an
electric cable, it would require nearly a whole day for a message to
pass.

Next, the time has also been measured which is required by a
nerve-centre to perform its part in a reflex action, where no thought or
consciousness is involved. This time, in the case of the winking reflex,
and apart from the time required for the passage of the molecular waves
up and down the sensory and motor nerves, is about 1/20 of a second.
Such is the rate at which a nerve-centre conducts its operations when no
consciousness or volition is involved. But when consciousness and
volition are involved, or when the cerebral hemispheres are called into
play, the time required is considerably greater. For the operations on
the part of the hemispheres which are comprised in perceiving a simple
sensation (such as an electrical shock) and the volitional act of
signalling the perception, cannot be performed in less than 1/12 of a
second, which is nearly twice as long as the time required by the lower
nerve-centres for the performance of a reflex action. Other experiments
prove that the more complex an act of perception, the more time is
required for its performance. Thus, when the experiment is made to
consist, not merely in signalling a perception, but in signalling one of
two or more perceptions (such as an electrical shock on one or other of
the two hands, which of five letters is suddenly exposed to view, &c.),
a longer time is required for the more complex process of distinguishing
which of the two or more expected stimuli is perceived, and in
determining which of the appropriate signals to make in response. The
time consumed by the cerebral hemispheres in meeting a 'dilemma' of this
kind is from 1/5 to 1/20 of a second longer than that which they consume
in the case of a simpler perception. Therefore, whenever mental
operations are concerned, a relatively much greater time is required for
a nerve-centre to perform its adjustments than when a merely mech