can we not say that the mainspring of the energy of living
bodies is the life that is in them?

Apart from the force exerted by living animal bodies, see the force
exerted by living plant bodies. I thought of the remark of Sir Oliver
one day not long after reading it, while I was walking in a beech wood
and noted how the sprouting beechnuts had sent their pale radicles down
through the dry leaves upon which they were lying, often piercing two
or three of them, and forcing their way down into the mingled soil and
leaf-mould a couple of inches. Force was certainly expended in doing
this, and if the life in the sprouting nut did not exert it or expend
it, what did?

When I drive a peg into the ground with my axe or mallet, is the life in
my arm any more strictly the source (the secondary source) of the energy
expended than is the nut in this case? Of course, the sun is the primal
source of the energy in both cases, and in all cases, but does not life
exert the force, use it, bring it to bear, which it receives from the
universal fount of energy?

Life cannot supply energy _de novo_, cannot create it out of nothing,
but it can and must draw upon the store of energy in which the earth
floats as in a sea. When this energy or force is manifest through a
living body, we call it vital force; when it is manifest through a
mechanical contrivance, we call it mechanical force; when it is
developed by the action and reaction of chemical compounds, we call it
chemical force; the same force in each case, but behaving so differently
in the one case from what it does in the other that we come to think of
it as a new and distinct entity. Now if Sir Oliver or any one else could
tell us what force is, this difference between the vitalists and the
mechanists might be reconciled.

Darwin measured the force of the downward growth of the radicle, such as
I have alluded to, as one quarter of a pound, and its lateral pressure
as much greater. We know that the roots of trees insert themselves into
seams in the rocks, and force the parts asunder. This force is
measurable and is often very great. Its seat seems to be in the soft,
milky substance called the cambium layer under the bark. These minute
cells when their force is combined may become regular rock-splitters.

One of the most remarkable exhibitions of plant force I ever saw was in
a Western city where I observed a species of wild sunflower forcing its
way up through the asphalt pavemen