e body, and would be
entirely useless. The axons of the sensory nerve divide into fine
branches in the sense organ, and thus are more easily aroused by the
stimulus.

Besides the sensory axons, two other things are often found in a sense
organ--sometimes one of the two, sometimes the other and sometimes
both. First, there are special sense cells in a few sense organs; and
second, in most sense organs there is accessory apparatus which,
without being itself sensitive, assists in bringing the stimulus to
the sense cells or sensory nerve ends.

[Illustration: Fig. 25.--Diagram of the taste end-organ. Within the
"Taste bud" are seen two sense cells, and around the base of these
cells are seen the terminations of two axons of the nerve of taste.
(Figure text: surface of tongue, taste bud, pit)]

_Sense cells_ are present only in the eye, ear, nose and mouth--always
in very sheltered situations. The taste cells are located in little
pits opening upon the surface of the tongue. In the sides of these
pits can be found little flask-shaped chambers, each containing a
number of taste cells. The taste cell has a slender prolongation that
protrudes from the chamber into the pit; and it is this slender tip of
the cell that is exposed to the chemical stimulus of the {190} tasting
substance. The stimulus arouses the taste cell, and this in turn
arouses the ending of the sensory axon that twines about the base of
the cell at the back of the chamber. The taste cell, or its tip, is
extra sensitive to chemical stimuli, and its activity, aroused by the
chemical stimulus, in turn arouses the axon and so starts a nerve
current to the brain stem and eventually to the cortex.

[Illustration: Fig. 26.--The olfactory sense cells and their brain
connections. (Figure text: axon to brain cortex, dendrites, synapses in
brain stem, axons of sense cells sense cells in nose.)]

The olfactory cells, located in a little recess in the upper and back
part of the nose, out of the direct air currents going toward the
lungs, are rather similar to the taste cells. They have fine tips
reaching to the surface of the mucous membrane lining the nasal cavity
and exposed to the chemical stimuli of odors. The olfactory cell has
also a long slender branch extending from its base through the bone
into the skull cavity and connecting there with dendrites of nerve
cells. This central branch of the olfactory cell is, in fact, an axon;
and it is peculiar in b