working together as a unit,
thus unifying and harmonizing our thoughts, emotions, and acts.

6. FORMS OF SENSORY STIMULI

Let us next inquire how this mechanism of the nervous system is acted
upon in such a way as to give us sensations. In order to understand
this, we must first know that all forms of matter are composed of minute
atoms which are in constant motion, and by imparting this motion to the
air or the ether which surrounds them, are constantly radiating energy
in the form of minute waves throughout space. These waves, or
radiations, are incredibly rapid in some instances and rather slow in
others. In sending out its energy in the form of these waves, the
physical world is doing its part to permit us to form its acquaintance.
The end-organs of the sensory nerves must meet this advance half-way,
and be so constructed as to be affected by the different forms of energy
which are constantly beating upon them.

[Illustration: FIG. 14.--The prism's analysis of a bundle of light rays.
On the right are shown the relation of vibration rates to temperature
stimuli, to light and to chemical stimuli. The rates are given in
billions per second.--After WITMER.]

THE END-ORGANS AND THEIR RESPONSE TO STIMULI.--Thus the radiations of
ether from the sun, our chief source of light, are so rapid that
billions of them enter the eye in a second of time, and the retina is of
such a nature that its nerve cells are thrown into activity by these
waves; the impulse is carried over the optic nerve to the occipital lobe
of the cortex, and the sensation of sight is the result. The different
colors also, from the red of the spectrum to the violet, are the result
of different vibration rates in the waves of ether which strike the
retina; and in order to perceive color, the retina must be able to
respond to the particular vibration rate which represents each color.
Likewise in the sense of touch the end-organs are fitted to respond to
very rapid vibrations, and it is possible that the different qualities
of touch are produced by different vibration rates in the atoms of the
object we are touching. When we reach the ear, we have the organ which
responds to the lowest vibration rate of all, for we can detect a sound
made by an object which is vibrating from twenty to thirty times a
second. The highest vibration rate which will affect the ear is some
forty thousand per second.

Thus it is seen that there are great gaps in the different ra