structure, like the eye, ear or nose, is played upon by a stimulus,
a chemical process of some kind is started which releases a neural
impulse in the system of conductors. This neural impulse passes
through the conductors, finally reaching the muscle or gland.
Under the action of this impulse, the muscle shortens or the
gland begins to secrete. The animal thus moves or acts. In
order to have these various mechanisms clearly before us, we
shall have to study (1) the sense organ side of man: the eye, the
ear, the senses of touch, olfaction, warmth, cold, pain, the organic
and the kinæsthetic; (2) the neural or conducting mechanism,
i.e., the peripheral and central nervous systems (and the sym-
pathetic nervous system); (3) the motor and glandular systems--
the effectors, consisting of the striped muscles which are under
the control of the peripheral and central nervous systems, and
the unstriped muscles and glands which are usually under the
control of the sympathetic. The student should formulate his
problem somewhat as follows: "(1) What extra-organic and
intra-organic stimuli will cause my subject, man, to act; how
can I arrange simple and complex situations which will cause
him to act in harmony with environmental demands? (2) From
my general reading it would appear that the function of the
stimulus is to arouse a neural impulse. I want to know for both
practical and theoretical reasons what the course of this neural
impulse is, i.e., how it finds a way to the muscle, because if there
happens to be a defect, either anatomical or functional in this
chain of conductors, I know that any stimulus I may apply will
not lead to the usual reaction. (3) In order to understand what
can be done with man in the way of establishing integrated sys-
tems of response, I must have at least an elementary knowledge
of the ways in which muscles, tendons and joints function: and
know something about the kinds of glands he has, and the
influence of these glands upon the muscles." The student who
has had no physiology will find it profitable to read straight
through the three chapters on the sense organs, the conductors,
and the muscles and glands, and then turn back and study in
detail the chapters in the order in which they appear. In our
study of the sense organs which immediately follows, we shall

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