origin of life must be of the origin of that machine. Are there any
forces in nature which are of a sort as to enable us to use them to
explain the building of machines? Plants and animals are the only
machines which nature has produced. They are the only instances in
nature of a structure built with its parts harmoniously adjusted to each
other to the performance of certain ends. All other machines with which
we are acquainted were made by man, and in making them intelligence came
in to adapt the parts to each other. But in the living organism is a
similarly adapted machine made by natural means rather than artificial.
How were they built? Does nature, apart from human intelligence, possess
forces which can achieve such results?

Here again we must attack the problem from what seems to be the wrong
end. Apparently it would be simpler to discover the method of the
manufacture of the simplest machine rather than the more complex ones.
But this has proved contrary to the fact. Perhaps the chief reason is
that the simplest living machine is the cell whose study must always
involve the use of the microscope, and for this reason is more
difficult. Perhaps it is because the problem is really a more difficult
one than to explain the building of the more complex machines out of the
simpler ones. At all events, the last fifty years have told us much of
the method of the building of the complex machines out of the simpler
ones, while we have as yet not even a hint as to the solution of the
building of the simplest machine from the inanimate world. Our attention
must, therefore, be first directed to the method by which nature has
constructed the complex machines which we find filling the world to-day
in the form of animals and plants.

==History of the Living Machine.==--In the first place, we must notice
that these machines have not been fashioned suddenly or rapidly, but
have been the result of a very slow growth. They have had a history
extending very far back into the past for a period of years which we can
only indefinitely estimate, but certainly reaching into the millions. As
we look over this past history in the light of our present knowledge we
see that whatever have been the forces which have been concerned in the
construction of these machines they have acted very slowly. It has taken
centuries, and, indeed, thousands of years, to take the successive steps
which have been necessary in this construction. Secondly, we no