anical
or non-mental response is needed; and the more complex the mental
operation the more time is necessary. Such may be termed the physiology
of deliberation.

So much, then, for the rate at which molecular movements travel through
nerves, and the times which nerve-centres consume in performing their
molecular adjustments. We may next consider the researches which have
been made within the last few months upon the rates of these movements
themselves, or the number of vibrations per second with which the
particles of nervous matter oscillate.

If, by means of a suitable apparatus, a muscle is made to record its own
contraction, we find that during all the time it is in contraction, it
is under-going a vibratory movement at the rate of about nine pulsations
per second. What is the meaning of this movement? The meaning is that
the act of will in the brain, which serves as a stimulus to the
contraction of the muscle, is accompanied by a vibratory movement in the
grey matter of the brain; that this movement is going on at the rate of
nine pulsations per second; and that the muscle is giving a separate or
distinct contraction in response to every one of these nervous
pulsations. That such is the true explanation of the rhythm in the
muscle is proved by the fact that if, instead of contracting a muscle by
an act of the will, it be contracted by means of a rapid series of
electrical shocks playing upon its attached nerve, the record then
furnished shows a similar trembling going on in the muscle as in the
previous case; but the tremors of contraction are now no longer at the
rate of nine per second: they correspond beat for beat with the
interruptions of the electrical current. That is to say, the muscle is
responding separately to every separate stimulus which it receives
through the nerve; and further experiment shows that it is able thus to
keep time with the separate shocks, even though these be made to follow
one another so rapidly as 1,000 per second. Therefore we can have no
doubt that the slow rhythm of nine per second under the influence of
volitional stimulation, represents the rate at which the muscle is
receiving so many separate impulses from the brain: the muscle is
keeping time with the molecular vibrations going on in the cerebral
hemispheres at the rate of nine beats per second. Careful tracings show
that this rate cannot be increased by increasing the strength of the
volitional stimulus; but some individu