A Practical Physiology | Page 2

language,--not one comes
home to us with such 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 those composing
the body, which are capable through a process called oxidation, or
through other chemical changes, of setting free a certain amount of
energy.
Again, our bodies are continually making heat and giving it out to
surrounding objects, the production and the loss of heat being so
adjusted that the whole body is warm, that is, of a temperature higher
than that of surrounding objects. Our bodies, also, move themselves,
either one part on another, or the whole body from place to place. The
motive power is not from the outside world, but the energy of their
movements exists in the bodies themselves, influenced by changes in
their surroundings. Finally, our bodies are continually getting rid of
so-called waste matters, which may be considered products of the
oxidation of the material used as food, or of the substances which make

up the organism.
4. The Main Problems of Physiology briefly Stated. We shall learn in a
subsequent chapter that the living body is continually losing energy,
but by means of food is continually restoring its substance and
replenishing its stock of energy. A great deal of energy thus stored up is
utilized as mechanical work, the result of physical movements. We
shall learn later on that much of the energy which at last leaves the
body as heat, exists for a time within the organism in other forms than
heat, though eventually transformed into heat. Even a slight change in
the surroundings of the living body may rapidly, profoundly, and in
special ways affect not only the amount, but the kind of energy set free.
Thus the mere touch of a hair may lead to such a discharge of energy,
that a body previously at rest may be suddenly thrown into violent
convulsions. This is especially true in the case of tetanus, or lockjaw.
The main problem we have to solve in the succeeding pages is to
ascertain how it is that our bodies can renew their substance and
replenish the energy which they are continually losing, and can,
according to the nature of their surroundings, vary not only the amount,
but the kind of energy which they set free.
5. Technical Terms Defined. All living