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.
