to account for the existence of this machine, for such a completed piece
of mechanism as a man or a tree cannot be explained as a result of
simple accident, as the existence of a rough piece of rock might be
explained. Its intricacy of parts and their purposeful interrelation
demands explanation, and therefore the fundamental problem is to explain
how this machine came into existence. The second problem is simpler, for
it is simply to explain the running of the machine after it is made. If
the organism is really a machine, we ought to be able to find some way
of explaining its actions as we can those of a steam engine.

Of these two problems the first is the more fundamental, for if we fail
to find an explanation for the existence of the machine, our explanation
of its method of action is only partly satisfactory. But the second
question is the simpler, and must be answered first. We cannot hope to
explain the more puzzling matter of the origin of the machine unless we
can first understand how it acts. In our treatment of the subject,
therefore, we shall divide it into two parts:

I. _The Running of the Living Machine_.

II. _The Origin of the Living Machine_.




PART I.

_THE RUNNING OF THE LIVING MACHINE._

* * * * *