one cause.  And that cause, I am convinced, is selfishness.  We wish to own, to dominate, to control, absolutely, entirely, for our own pleasure, and satisfaction, that of which we are jealous.  In Chapter One I tell the incident of the young man on the street car whose jealous worry was so manifest when he saw his “girl” smiling upon another man.  I suppose most men and women feel, or have felt, at some time or other, this sex jealousy.  That woman belongs to me, her smiles are mine, her pleasant words should fall on my ear alone; I am her lover, she, the mistress of my heart; and that should content her.

Every writer of the human heart has expatiated upon this great source of worry—­jealousy.  Shakspere refers to it again and again.  The whole play of Othello rests upon the Moor’s jealousy of his fair, sweet, and loyally faithful Desdemona.  How the fiendish Iago plays upon Othello’s jealous heart until one sees that: 

  Trifles, light as air,
  Are to the jealous confirmations strong
  As proofs of holy writ.

Iago bitterly resents a slight he feels Othello has put upon him.  With his large, generous, unsuspicious nature, Othello never dreams of such a thing; he trusts Iago as his intimate friend, and thus gives the crafty fiend the oportunity he desires to

          put the Moor
  Into a jealousy so strong
  That judgment cannot cure ... 
  Make the Moor thank me, love me, reward me,
  For making him egregiously an ass
  And practicing upon his peace and quiet
  Even to madness.

Othello gives his wife, Desdemona, a rare handkerchief.  Iago urges his own wife, who is Desdemona’s maid, to pilfer this and bring it to him.  When he gets it, he leaves it in Cassio’s room.  Cassio was an intimate friend of Othello’s, one, indeed, who had gone with him when he went to woo Desdemona, and who, by Iago’s machinations, had been suspended from his office of Othello’s chief lieutenant.  To provoke Othello’s jealousy Iago now urges Desdemona to plead Cassio’s cause with her husband, and at the came time eggs on Othello to watch Cassio: 

Look to your wife; observe her well with Cassio;
Wear your eye thus, not jealous nor secure. 
I would not have your free and noble nature
Out of self-bounty be abus’d; look to ’t.

Thus he works Othello up to a rage, and yet all the time pretends to be holding him back: 

         I do see you’re mov’d;
  I pray you not to strain my speech
  To grosser issues nor to larger reach
  Than to suspicion.

Iago leaves the handkerchief in Cassio’s room, at the same time saying: 

The Moor already changes with my poison;
Dangerous conceits are in their natures poisons,
Which at the first are scarce found to distaste,
But with a little act upon the blood,
Burn like the mines of sulphur.