of the mind.  The truly novel in the content of the idea is the recognition of the fact that the wish is charged.  Now it could never be charged in a vacuum.  That means that a wish could never be born in the brain alone.  For the brain has no power to charge itself with energy—­it can only store and transmit.  If a wish is potential energy that must be transformed into kinetic, it must have a source.  That source is the vegetative system.  Without the vegetative system, the great complex of viscera in the abdomen and chest, blood and its vessels, endocrines, muscles and nerves, the brain would remain but an intricate cold storage plant of memories, associations of past experiences.  It would need no change and initiate no effort.  But when the wish enters upon the scene, it is as if a dead storage battery has been refreshed with new current.  Enriched with billions of electrons there is a stir and a movement, dynamic mind.  But the dynamo is the more ancient possession of the animal, the vegetative apparatus.  In short, what must always be remembered is that a wish is never cerebral, but always sub-cerebral, visceral, in its origins.

The sub-cerebral makes the cerebral.  Activities in the nervous system below the brain and especially the vegetative system, force upon it its function of the active verb.  It has to be, to do, and to suffer, and then to manipulate the environment to satiate the insatiable viscera, insatiable because the local chemistry is continually raising the tension of one or the other of them.  A physics of human behaviour becomes possible with the aid of these concepts of endocrine regulation of intravisceral pressure, and intervisceral equilibrium, an intramuscular pressure and an intermuscular equilibrium, with the brain as the shifting fulcrum of the system.

The sensation of hunger, as we have seen, serves as good an exemplar as any of this mechanism of the wish.  Hunger is preceded and accompanied by contractions of the stomach of increasing intensity.  Those contractions must be brought about by a substance acting upon the nerve endings in the wall of the stomach.  As it closes down upon itself, waves pass up and down.  With each wave, the pressure within it rises.  The exact amount of the pressure may be accurately measured by means of a small balloon swallowed and then inflated.  When the pressure rises above a certain figure, the sensation of hunger breaks into the consciousness of the individual.  We infer that certain sensory impulses sent up to the brain attain a strength that finally forces itself into the conscious field of feeling.  The sensation of hunger varies from individual to individual because of variation in the reaction throughout the vegetative system.  Most often it is a sense of movement or even an itch in the upper abdomen.  Let some cause produce a weakening or cessation of the movements of the stomach—­as fear and anger—­and the sensation of hunger disappears coincidently with the drop in the pressure within it.  As the mathematicians would say, the wish is a function of the pressure, and so of the concentration of substance behind the pressure.