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,