Teachers know, and students soon learn to recognize the fact, that it is
impossible to obtain a clear understanding of the functions of the various
parts of the body without first mastering a few elementary facts about
their structure. The course adopted, therefore, in this book, is to devote
a certain amount of space to the anatomy of the several organs before
describing their functions.

A mere knowledge of the facts which can be gained in secondary schools,
concerning the anatomy and physiology of the human body, is of little real
value or interest in itself. Such facts are important and of practical
worth to young students only so far as to enable them to understand the
relation of these facts to the great laws of health and to apply them to
daily living. Hence, it has been the earnest effort of the author in this
book, as in his other physiologies for schools, to lay special emphasis
upon such points as bear upon personal health.

Physiology cannot be learned as it should be by mere book study. The
result will be meagre in comparison with the capabilities of the subject.
The study of the text should always be supplemented by a series of
practical experiments. Actual observations and actual experiments are as
necessary to illuminate the text and to illustrate important principles in
physiology as they are in botany, chemistry, or physics. Hence, as
supplementary to the text proper, and throughout the several chapters, a
series of carefully arranged and practical experiments has been added. For
the most part, they are simple and can be performed with inexpensive and
easily obtained apparatus. They are so arranged that some may be omitted
and others added as circumstances may allow.

If it becomes necessary to shorten the course in physiology, the various
sections printed in smaller type may be omitted or used for home study.