the whole process from beginning to end. It would see every
molecule placed in its position by the specific attractions and
repulsions exerted between it and other molecules, the whole process,
and its consummation, being an instance of the play of molecular
force. Given the grain and its environment, with their respective
forces, the purely human intellect might, if sufficiently expanded,
trace out _a priori_ every step of the process of growth, and, by the
application of purely mechanical principles, demonstrate that the
cycle must end, as it is seen to end, in the reproduction of forms
like that with which it began. A necessity rules here, similar to
that which rules the planets in their circuits round the sun.

You will notice that I am stating the truth strongly, as at the
beginning we agreed it should be stated. But I must go still further,
and affirm that in the eye of science the animal body is just as much
the product of molecular force as the chalk and the ear of corn, or as
the crystal of salt or sugar. Many of the parts of the body are
obviously mechanical. Take the human heart, for example, with its
system of valves, or take the exquisite mechanism of the eye or hand.
Animal heat, moreover, is the same in kind as the heat of a fire,
being produced by the same chemical process. Animal motion, too, is
as certainly derived from the food of the animal, as the motion of
Trevethyck's walking-engine from the fuel in its furnace. As regards
matter, the animal body creates nothing; as regards force, it creates
nothing. Which of you by taking thought can add one cubit to his
stature? All that has been said, then, regarding the plant, may be
restated with regard to the animal. Every particle that enters into
the composition of a nerve, a muscle, or a bone, has been placed in
its position by molecular force. And unless the existence of law in
these matters be denied, and the element of caprice introduced, we
must conclude that, given the relation of any molecule of the body to
its environment, its position in the body might be determined
mathematically. Our difficulty is not with the _quality_ of the
problem, but with its _complexity_; and this difficulty might be met by
the simple expansion of the faculties we now possess. Given this
expansion, with the necessary molecular data, and the chick might be
deduced as rigorously and as logically from the egg, as the existence
of Neptune from the disturbances o