peculiar interest as does physiology, because
this is the study of ourselves.

Every thoughtful young person must have asked himself a hundred questions
about the problems of human life: how it can be that the few articles of
our daily food--milk, bread, meats, and similar things--build up our
complex bodies, and by what strange magic they are transformed into hair,
skin, teeth, bones, muscles, and blood.

How is it that we can lift these curtains of our eyes and behold all the
wonders of the world around us, then drop the lids, and though at noonday,
are instantly in total darkness? How does the minute structure of the ear
report to us with equal accuracy the thunder of the tempest, and the hum
of the passing bee? Why is breathing so essential to our life, and why
cannot we stop breathing when we try? Where within us, and how, burns the
mysterious fire whose subtle heat warms us from the first breath of
infancy till the last hour of life?

These and scores of similar questions it is the province of this deeply
interesting study of physiology to answer.

2. What Physiology should Teach us. The study of physiology is not
only interesting, but it is also extremely useful. Every reasonable person
should not only wish to acquire the knowledge how best to protect and
preserve his body, but should feel a certain profound respect for an
organism so wonderful and so perfect as his physical frame. For our bodies
are indeed not ourselves, but the frames that contain us,--the ships in
which we, the real selves, are borne over the sea of life. He must be
indeed a poor navigator who is not zealous to adorn and strengthen his
ship, that it may escape the rocks of disease and premature decay, and
that the voyage of his life may be long, pleasant, and successful.

But above these thoughts there rises another,--that in studying physiology
we are tracing the myriad lines of marvelous ingenuity and forethought, as
they appear at every glimpse of the work of the Divine Builder. However
closely we study our bodily structure, we are, at our best, but imperfect
observers of the handiwork of Him who made us as we are.

3. Distinctive Characters of Living Bodies. Even a very meagre
knowledge of the structure and action of our bodies is enough to reveal
the following distinctive characters: our bodies are continually
breathing, that is, they take in oxygen from the surrounding air; they
take in certain substances known as food, similar to t