es of chemistry and physics cannot account for? Are there
limits to the application of natural law to explain life? Can there be
found something connected with living beings which is force but not
correlated with the ordinary forms of energy? Is there such a thing as
_vital energy_, or is the so-called vital force simply a name which we
have given to the peculiar manifestations of ordinary energy as shown in
the substance protoplasm? These are some of the questions that modern
biology is trying to answer, and it is the existence of such questions
which has made modern biology a new science. Such questions not only did
not, but could not, have arisen before the doctrines of the conservation
of energy and evolution had made their impression upon the thought of
the world.

==Significance of the New Biological Problems==--It is further evident
that the answers to these questions will have a significance reaching
beyond the domain of biology proper and affecting the fundamental
philosophy of nature. The answer will determine whether or not we can
accept in entirety the doctrines of the conservation of energy and
evolution. Plainly if it should be found that the energy of animate
nature was not correlated with other forms of energy, this would demand
either a rejection or a complete modification of our doctrine of the
conservation of energy. If an animal can create any energy within
itself, or can destroy any energy, we can no longer regard the amount of
energy of the universe as constant. Even if that subtile form of force
which we call nervous energy should prove to be uncorrelated with other
forms of energy, the idea of the conservation of energy must be changed.
It is even possible that we must insist that the still more subtile form
of force, mental force, must be brought within the scope of this great
law in order that it be implicitly accepted. This law has proved itself
strictly applicable to the inanimate world, and has then thrust upon us
the various questions in regard to vital force, and we must recognize
that the real significance of this great law must rest upon the
possibility of its application to vital phenomena.

No less intimate is the relation of these problems to the doctrine of
evolution. Evolution tries to account for each moment in the history of
the world as the result of the conditions of the moment before. Such a
theory loses its meaning unless it can be shown that natural forces are
sufficient to