Our daily lives go on for the most part in two worlds, the world of
mechanical transposition and the world of chemical transformations, but
we are usually conscious only of the former. This is the visible,
palpable world of motion and change that rushes and roars around us in
the winds, the storms, the floods, the moving and falling bodies, and
the whole panorama of our material civilization; the latter is the
world of silent, invisible, unsleeping, and all-potent chemical
reactions that take place all about us and is confined to the atoms and
molecules of matter, as the former is confined to its visible
aggregates.
Mechanical forces and chemical affinities rule our physical lives, and
indirectly our psychic lives as well. When we come into the world and
draw our first breath, mechanics and chemistry start us on our career.
Breathing is a mechanical, or a mechanico-vital, act; the mechanical
principle involved is the same as that involved in the working of a
bellows, but the oxidation of the blood when the air enters the lungs is
a chemical act, or a chemico-vital act. The air gives up a part of its
oxygen, which goes into the arterial circulation, and its place is taken
by carbonic-acid gas and watery vapor. The oxygen feeds and keeps going
the flame of life, as literally as it feeds and keeps going the fires in
our stoves and furnaces.
Hence our most constant and vital relation to the world without is a
chemical one. We can go without food for some days, but we can exist
without breathing only a few moments. Through these spongy lungs of ours
we lay hold upon the outward world in the most intimate and constant
way. Through them we are rooted to the air. The air is a mechanical
mixture of two very unlike gases--nitrogen and oxygen; one very inert,
the other very active. Nitrogen is like a cold-blooded, lethargic
person--it combines with other substances very reluctantly and with but
little energy. Oxygen is just its opposite in this respect: it gives
itself freely; it is "Hail, fellow; well met!" with most substances, and
it enters into co-partnership with them on such a large scale that it
forms nearly one half of the material of the earth's crust. This
invisible gas, this breath of air, through the magic of chemical
combination, forms nearly half the substance of the solid rocks. Deprive
it of its affinity for carbon, or substitute nitrogen or hydrogen in its
place, and the air would quickly suffocate us. That changing of the dark
venous blood in our lungs into the bright, red, arterial blood would
instantly cease. Fancy the sensation of inhaling an odorless,
non-poisonous atmosphere that would make one gasp for breath! We should
be quickly poisoned by the waste of our own bodies. All things that live
must have oxygen, and all things that burn must have oxygen. Oxygen does
not burn, but it supports combustion.
And herein is one of the mysteries of chemistry again. This support
which the oxygen gives is utterly unlike any support we are acquainted
with in the world of mechanical forces. Oxygen supports combustion by
combining chemically with carbon, and the evolution of heat and light is
the result. And this is another mystery--this chemical union which takes
place in the ultimate particles of matter and which is so radically
different from a mechanical mixture. In a chemical union the atoms are
not simply in juxtaposition; they are, so to speak, inside of one
another--each has swallowed another and lost its identity, an impossible
feat, surely, viewed in the light of our experiences with tangible
bodies. In the visible, mechanical world no two bodies can occupy the
same place at the same time, but apparently in chemistry they can and
do. An atom of oxygen and one of carbon, or of hydrogen, unite and are
lost in each other; it is a marriage wherein the two or three become
one. In dealing with the molecules and atoms of matter we are in a world
wherein the laws of solid bodies do not apply; friction is abolished,
elasticity is perfect, and place and form play no part. We have escaped
from matter as we know it, the solid, fluid, or gaseous forms, and are
dealing with it in its fourth or ethereal estate. In breathing, the
oxygen goes into the blood, not to stay there, but to unite with and
bring away the waste of the system in the shape of carbon, and re-enter
the air again as one of the elements of carbonic-acid gas, CO_{2}. Then
the reverse process takes place in the vegetable world, the leaves
breathe this poisonous gas, release the oxygen under the chemistry of
the sun's rays, and appropriate and store up the carbon. Thus do the
animal and vegetable worlds play into each other's hands. The animal is
dependent upon the vegetable for its carbon, which it releases again,
through the life processes, as carbonic-acid gas, to be again drawn into
the cycle of vegetable life.
The act of breathing well illustrates our mysterious relations to
Nature--the cunning way in which she plays the principal part in our
lives without our knowledge. How certain we are that we draw the air
into our lungs--that we seize hold of it in some way as if it were a
continuous substance, and pull it into our bodies! Are we not also
certain that the pump sucks the water up through the pipe, and that we
suck our iced drinks through a straw? We are quite unconscious of the
fact that the weight of the superincumbent air does it all, that
breathing is only to a very limited extent a voluntary act. It is
controlled by muscular machinery, but that machinery would not act in a
vacuum. We contract the diaphragm, or the diaphragm contracts under
stimuli received through the medulla oblongata from those parts of the
body which constantly demand oxygen, and a vacuum tends to form in the
chest, which is constantly prevented by the air rushing in to fill it.
The expansive force of the air under its own weight causes the lungs to
fill, just as it causes the bellows of the blacksmith to fill when he
works the lever, and the water to rise in the pump when we force out the
air by working the handle. Another unconscious muscular effort under the
influence of nerve stimulus, and the air is forced out of the lungs,
charged with the bodily waste which it is the function to relieve. But
the wonder of it all is how slight a part our wills play in the process,
and how our lives are kept going by a mechanical force from without,
seconded or supplemented by chemical and vital forces from within.
The one chemical process with which we are familiar all our lives, but
which we never think of as such, is fire. Here on our own hearthstones
goes on this wonderful spectacular and beneficent transformation of
matter and energy, and yet we are grown so familiar with it that it
moves us not. We can describe combustion in terms of chemistry, just as
we can describe the life-processes in similar terms, yet the mystery is
no more cleared up in the one case than in the other. Indeed, it seems
to me that next to the mystery of life is the mystery of fire. The
oxidizing processes are identical, only one is a building up or
integrating process, and the other is a pulling down or disintegrating
process. More than that, we can evoke fire any time, by both mechanical
and chemical means, from the combustible matter about us; but we cannot
evoke life. The equivalents of life do not slumber in our tools as do
the equivalents of fire. Hence life is the deeper mystery. The ancients
thought of a spirit of fire as they did of a spirit of health and of
disease, and of good and bad spirits all about them, and as we think of
a spirit of life, or of a creative life principle. Are we as wide of
the mark as they were? So think many earnest students of living things.
When we do not have to pass the torch of life along, but can kindle it
in our laboratories, then this charge will assume a different aspect.