a mental effort does not appear again in the circuit of the law of the conservation of energy.  A man uses up more energy in his waking moments, though his body be passive, than in his sleeping.  What we call mental force cannot be accounted for in terms of physical force.  The sun’s energy goes into our bodies through the food we eat, and so runs our mental faculties, but how does it get back again into the physical realm?  Science does not know.

It must be some sort of energy that lights the lamps of the firefly and the glow-worm, and it must be some sort or degree of energy that keeps consciousness going.  The brain of a Newton, or of a Plato, must make a larger draft on the solar energy latent in food-stuffs than the brain of a day laborer, and his body less.  The same amount of food-consumption, or of oxidation, results in physical force in the one case, and mental force in the other, but the mental force escapes the great law of the equivalence of the material forces.

John Fiske solves the problem when he drops his physical science and takes up his philosophy, declaring that the relation of the mind to the body is that of a musician to his instrument, and this is practically the position of Sir Oliver Lodge.

Inheritance and adaptation, says Haeckel, are sufficient to account for all the variety of animal and vegetable forms on the earth.  But is there not a previous question?  Do we not want inheritance and adaptation accounted for?  What mysteries they hold!  Does the river-bed account for the river?  How can a body adapt itself to its environment unless it possess an inherent, plastic, changing, and adaptive principle?  A stone does not adapt itself to its surroundings; its change is external and not internal.  There is mechanical adjustment between inert bodies, but there is no adaptation without the push of life.  A response to new conditions by change of form implies something actively responsive—­something that profits by the change.

VII

If we could tell what determines the division of labor in the hive of bees or a colony of ants, we could tell what determines the division of labor among the cells in the body.  A hive of bees and a colony of ants is a unit—­a single organism.  The spirit of the body, that which regulates all its economies, which directs all its functions, which cooerdinates its powers, which brings about all its adaptations, which adjusts it to its environment, which sees to its repairs, heals its wounds, meets its demands, provides more force when more is needed, which makes one organ help do the work of another, which wages war on disease germs by specific ferments, which renders us immune to this or that disease; in fact, which carries on all the processes of our physical life without asking leave or seeking counsel of us,—­all this is on another plane from the mechanical or chemical—­super-mechanical.