ymes, or
ferments, in all living bodies, but it does not know the secret of these
ferments; it knows the part played by colloids, or jelly-like compounds,
that there is no living body without colloids, though there are colloid
bodies that are not living; it knows the part played by oxidation, that
without it a living body ceases to function, though everywhere all about
us is oxidation without life; it knows the part played by chlorophyll in
the vegetable kingdom, and yet how chlorophyll works such magic upon the
sun's rays, using the solar energy to fix the carbon of carbonic acid in
the air, and thereby storing this energy as it is stored in wood and
coal and in much of the food we consume, is a mystery. Chemistry cannot
repeat the process in its laboratories. The fungi do not possess this
wonderful chlorophyllian power, and hence cannot use the sunbeam to
snatch their carbon from the air; they must get it from decomposed
vegetable matter; they feed, as the animals do, upon elements that have
gone through the cycle of vegetable life. The secret of vegetable life,
then, is in the green substance of the leaf where science is powerless
to unlock it. Conjure with the elements as it may, it cannot produce the
least speck of living matter. It can by synthesis produce many of the
organic compounds, but only from matter that has already been through
the organic cycle. It has lately produced rubber, but from other
products of vegetable life.

As soon as the four principal elements, carbon, oxygen, hydrogen, and
nitrogen, that make up the living body, have entered the world of living
matter, their activities and possible combinations enormously increase;
they enter into new relations with one another and form compounds of
great variety and complexity, characterized by the instability which
life requires. The organic compounds are vastly more sensitive to light
and heat and air than are the same elements in the inorganic world. What
has happened to them? Chemistry cannot tell us. Oxidation, which is only
slow combustion, is the main source of energy in the body, as it is in
the steam-engine. The storing of the solar energy, which occurs only in
the vegetable, is by a process of reduction, that is, the separation of
the carbon and oxygen in carbonic acid and water. The chemical reactions
which liberate energy in the body are slow; in dead matter they are
rapid and violent, or explosive and destructive. It is the chemistry in
the l