at the expense of part of the total store of energy.

Hence, as the phenomena exhibited by living beings, in so far as they
are material, are all molar or molecular motions, these are included
under the general law. A living body is a machine by which energy is
transformed in the same sense as a steam-engine is so, and all its
movements, molar and molecular, are to be accounted for by the energy
which is supplied to it. The phenomena of consciousness which arise,
along with certain transformations of energy, cannot be interpolated
in the series of these transformations, inasmuch as they are not
motions to which the doctrine of the conservation of energy applies.
And, for the same reason, they do not necessitate the using up of
energy; a sensation has no mass and cannot be conceived to be
susceptible of movement. That a particular molecular motion does give
rise to a state of consciousness is experimentally certain; but the
how and why of the process are just as inexplicable as in the case of
the communication of kinetic energy by impact.

When dealing with the doctrine of the ultimate constitution of matter,
we found a certain resemblance between the oldest speculations and the
newest doctrines of physical philosophers. But there is no such
resemblance between the ancient and modern views of motion and its
causes, except in so far as the conception of attractive and repulsive
forces may be regarded as the modified descendant of the Aristotelian
conception of forms. In fact, it is hardly too much to say that the
essential and fundamental difference between ancient and modern
physical science lies in the ascertainment of the true laws of statics
and dynamics in the course of the last three centuries; and in the
invention of mathematical methods of dealing with all the consequences
of these laws. The ultimate aim of modern physical science is the