There has grown up, contemporaneously with the teachings of Freud, a body of discoveries and knowledge in physiology, concerning these factors, which is like a long sword of light illuminating a pitch-black spot in the night.  The dark places in human nature seem to have become the sole monopoly of the Freudians and their psychology.  But only seemingly.  For all this time the physiologist has been working.  Beginning with a candle and now holding in his hands the most powerful arc-lights, he has explored two regions, the sympathetic nervous system and the glands of internal secretion, and has come upon data which in due course will render a good many of the Freudian dicta obsolete.  Not that the Freudian fundamentals will be scrapped completely.  But they will have to fit into the great synthesis which must form the basis of any control of the future of human nature.  That future belongs to the physiologist.  Already his achievements provide the foundations.  I propose in the following chapters to sketch the history and outline the elements of this new knowledge, and then to glimpse some of the larger human reactions to it.  A good deal of this new knowledge is not altogether new.  A number of the isolated facts have been known and talked about for more than two generations.  But the newer additions, and the light they have thrown upon old problems present the opportunity for a synthesis, which must sooner or later be made.

THE CHEMISTRY OF THE SOUL

Besides, it is time that the secrets of the laboratories stepped out into the market place, unashamed.  Imaginative man has played for ages immemorial with wondrous fairy tales and fancies of what he would achieve.  The sciences of physics and chemistry have made everyday commonplace realities out of his radiant dreams.  One need not repeat the cliches of our editors.  But the analogy is there nevertheless.  No control over heat and light and electricity, today our slaves, was possible until physics and chemistry took them in hand.  No control of the human soul is possible until it too will be taken in hand by them.  We may now look forward to a real future for mankind because we have before us the beginnings of a chemistry of human nature.  The internal secretions, with their influence upon brain and nervous system as well as every other part of the body corporation, as essentially blood-circulating chemical substances, have been discovered the real governors and arbiters of instincts and dispositions, emotions and reactions, characters and temperaments, good and bad.  A huge complex of evidence, as various, complicated and obscure as human nature itself, supports that fundamental law.