still confronted with the machinery of the cell.

But our analysis can not, at present, go further. Our knowledge of this
machine has not as yet enabled us to gain any insight as to its method
of action. We can not yet conceive how this machine controls the
chemical and physical forces at its disposal in such a way as to produce
the orderly result of life. The strict correlation between the forces of
the physical universe and those manifested by this protoplasm tells us
that a transformation of energy occurs within it, but of the method of
that transformation we as yet know nothing. Irritability, movement,
metabolism, and reproduction appear to be not chemical properties of a
compound, but mechanical properties of a machine. Our mechanical
analysis of the living machine stops short before it reaches any
foundation in the chemical forces of nature.

It is thus clearly apparent that the phenomena of life are dependent
upon the machinery of living things, and we have therefore the second
question of the _origin_ of this machinery to answer. Chemical forces
and mechanical forces have been laboriously investigated, but neither
appear adequate to the manufacture of machines. They produce only
chemical compounds and worlds with their mountains and seas. The
construction of artificial machines has demanded intelligence. But here
is a natural machine--the organism. It is the only machine produced by
natural methods, so far as we know; and we have therefore next asked
whether there are, in nature, simple forces competent to build machines
such as living animals and plants?

In pursuance of this question we have found that the complicated
machines have been built out of the simpler ones by the action of known
forces and laws. The factors in this machine building are simply those
of the fundamental vital properties of the simplest protoplasmic
machine. Reproduction, heredity, and variation, acting under the
ever-changing conditions of the earth's surface, are apparently all that
are needed to explain the building of the complex machines out of the
simpler ones. Nature _has_ forces adequate to the building of machines
as well as forces adequate to the formation of chemical compounds and
worlds.

But here again we are unable to base our explanation upon chemical and
physical forces. Reproduction, heredity, and variation are properties of
the cell machine, and we are therefore thrown back upon the necessity of
explaining the origi