ning intelligence, the organ
of consciousness.

[Sidenote: _Laboratory Proof of Sense-Perceptive Process_]

And you may set it down as an established principle that _all states
of consciousness, whether seemingly localized on the surface of the
body or not, are connected with the brain as the dominant center_.

The facts we have been recounting have been established by the
experiments of physiological psychology. Thus, the work of the
laboratory has shown that between the moment when a sense vibration
reaches the body and the moment when sensation occurs a measurable
interval of time intervenes.

If your eyes were to be blindfolded and your hand unexpectedly
pricked with a white-hot needle, the time that would elapse before
you could jerk your hand away could be readily measured in fractions
of a second with appropriate instruments.

[Sidenote: _Reaction Time_]

This interval is known as _reaction-time_. It varies greatly with
different persons. During this reaction-time, the cell or cells
attacked upon the surface of the hand have conveyed news of the
assault through numberless intermediate sensory nerve cells to
the brain. The brain in turn has sent out its mandate through the
appropriate motor nerve cells to all the muscle and other cells
surrounding the injured cell, commanding them to remove it from
the point of danger.

The work of the nervous system in dealing with the ether vibrations
that are constantly impinging upon the surface of the body has been
likened to that of the transmitter, connecting wire and receiver
of a telephone. Air-waves striking against the transmitter of the
telephone awaken a similar vibratory movement in the transmitter
itself. This movement is passed along the wire to the receiver,
which vibrates responsively and imparts a corresponding wave-like
motion to the air.

[Sidenote: _The Human Telephone_]

These air-waves when heard are what we call _sound_.

In the same way, air-waves striking the ear are communicated by
the auditory nerve to the brain, where they awaken a corresponding
sensation of sound. But these waves must be vibrating at between
30 and 20,000 times a second. If they are vibrating so slowly or
so rapidly as not to come within this range, we cannot hear them.

[Sidenote: _The Living Telegraph_]

This process is by no means a mechanical affair. On the contrary,
it is a series of _mental_ acts. Every cell in the living telegraph
must receive the message and