ery subject to adaptation. On first entering a
room you clearly sense an odor that you can no longer get after
staying there for some time. This adaptation to one odor does not
prevent your sensing quite different odors. Taste shows less
adaptation than smell, but all are familiar with the decline in sweet
sensation that comes with continued eating of sweets.

All of the cutaneous senses except that for pain are much subject to
adaptation. Continued steady pressure gives a sensation that declines
rapidly and after a time ceases altogether. The temperature sense is
usually adapted to the temperature of the skin, which therefore feels
neither warm nor cool. If the temperature of the skin is raised from
its usual level of about 70 degrees Fahrenheit to 80 or 86, this
temperature at first gives the sensation of warmth, but after a time
it gives no temperature sensation at all; the warmth sense has become
adapted to the temperature of 80 degrees; and now a temperature of 70
will give the sensation of cool. {225} Hold one hand in water at 80
and the other in water at 66, and when both have become adapted to
these respective temperatures, plunge them together into water at 70;
and you will find this last to feel cool to the warm-adapted hand and
warm to the cool-adapted. There are limits to this power of
adaptation.

The muscle sense seems to become adapted to any fixed position of a
limb, so that, after the limb has remained motionless for some time,
you cannot tell in what position it is; to find out, you have only to
move it the least bit, which will excite both the muscle sense and the
cutaneous pressure sense. The sense of head rotation is adaptable, in
that a rotation which is keenly sensed at the start ceases to be felt
as it continues; but here it is not the sense cells that become
adapted, but the back flow that ceases, as will soon be explained.

To come now to the sense of sight, we have _light adaptation, dark
adaptation_, and _color adaptation_. Go into a dark room, and at first
all seems black, but by degrees--provided there is a little light
filtering into the room--you begin to see, for your retina is becoming
dark-adapted. Now go out into a bright place, and at first you are
"blinded", but you quickly "get used" to the bright illumination and
see objects much more distinctly than at first; for your eye has now
become light-adapted. Remain for some time in a room illuminated by a
colored light (as the yellow