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.