achine is the same whether it is in action or repose, but when a body
ceases to function, it is not the same. It cannot be set going like a
machine; the motor power has ceased to be. But if the life of the body
were no more than the sum of the reactions existing between the body and
the medium in which it lives, this were not so. A body lives as long as
there is a proper renewal of the interior medium through exchanges with
its environment.

Mechanical principles are operative in every part of the body--in the
heart, in the arteries, in the limbs, in the joints, in the bowels, in
the muscles; and chemical principles are operative in the lungs, in the
stomach, in the liver, in the kidneys; but to all these things do we not
have to add something that is not mechanical or chemical to make the
man, to make the plant? A higher mechanics, a higher chemistry, if you
prefer, a force, but a force differing in kind from the physical forces.

The forces of life are constructive forces, and work in a world of
disintegrating or destructive forces which oppose them and which they
overcome. The mechanical and the chemical forces of dead matter are the
enemies of the forces of life till life overcomes and uses them; as much
so as gravity, fire, frost, water are man's enemies till he has learned
how to subdue and use them.

IV

It is a significant fact that the four chief elements which in various
combinations make up living bodies are by their extreme mobility well
suited to their purpose. Three of these are gaseous; only the carbon is
a solid. This renders them facile and adaptive in the ever-changing
conditions of organic evolution. The solid carbon forms the vessel in
which the precious essence of life is carried. Without carbon we should
evaporate or flow away and escape. Much of the oxygen and hydrogen
enters into living bodies as water; nine tenths of the human body is
water; a little nitrogen and a few mineral salts make up the rest. So
that our life in its final elements is little more than a stream of
water holding in solution carbonaceous and other matter and flowing,
forever flowing, a stream of fluid and solid matter plus something else
that scientific analysis cannot reach--some force or principle that
combines and organizes these elements into the living body.

If a man could be reduced instantly into his constituent elements we
should see a pail or two of turbid fluid that would flow down the bank
and soon be lost